Adaptive panoramic video streaming using composite pictures

ABSTRACT

Innovations in stream configuration operations and playback operations for adaptive streaming of panoramic video are described. The innovations include features of adaptive streaming of panoramic video with composite pictures. For example, a stream configuration tool splits an input picture of panoramic video into multiple sections and creates multiple composite pictures. A composite picture includes one of the sections as well as a low-resolution version of the input picture. A playback tool reconstructs one or more composite pictures. Under normal operation, the playback tool can use the reconstructed section(s) of the composite picture(s) to render high-quality views of the panoramic video. If the view window dramatically changes, however, or if encoded data for a section is lost or corrupted, the playback tool can use the low-resolution version of the input picture to render lower-quality details for views of the panoramic video, without disruption of playback.

BACKGROUND

When video is streamed over the Internet and played back through a Webbrowser or media player, the video is delivered in digital form. Digitalvideo is also used when video is delivered through many broadcastservices, satellite services and cable television services. Real-timevideoconferencing often uses digital video, and digital video is usedduring video capture with most smartphones, Web cameras and other videocapture devices. Digital video is also used for technologies such asvirtual reality (“VR”) and augmented reality (“AR”), whether video isplayed back in a head-mounted display, mobile device, or other type ofdevice.

Panoramic video is video in which views in multiple directions around acentral position are recorded at the same time. The recorded video caninclude image content in every direction, or at least image content inevery direction in a 360-degree circle around the central position, aswell as at least some image content above the central position and atleast some image content underneath the central position. Panoramicvideo is sometimes called 360-degree video, immersive video, orspherical video. Panoramic video can be captured using anomnidirectional camera or a collection of multiple cameras pointing indifferent directions. For modern-day applications, panoramic video isprocessed in digital form during stages of creation, editing, anddelivery, as well as stages of reconstruction and rendering forplayback.

During playback, a viewer typically can control a view directionrelative to the central position, potentially changing which section ofthe panoramic video is viewed over time. In some systems, a viewer canalso zoom in or zoom out. When panoramic video is rendered for display,the section of the panoramic video that is viewed may be projected to aflat image for output. For a mobile device or computer monitor, a singleoutput picture may be rendered. For a head-mounted display (or mobiledevice held in a head-mounted band), the section of the panoramic videothat is viewed may be projected to two output pictures, for the left andright eyes, respectively.

When a playback tool reconstructs and renders panoramic video, resourcesmay be wasted retrieving and reconstructing image content that is notviewed. For example, memory may be used to store sample values for areasof the panoramic video that are not viewed, and processing cycles may beused to determine the non-viewed sample values and their locations atdifferent stages of processing.

To use fewer resources, a playback tool may retrieve and reconstructonly part (not all) of the panoramic video. For example, considering theview direction and zoom factor for a viewer, the playback tool mayretrieve encoded data and reconstruct panoramic video just for thosesections of the panoramic video that are visible. In this way, theplayback tool may save memory, processing cycles, and other resourceswhile correctly rendering the visible sections of the panoramic video.If the view direction or zoom factor changes, however, the playback toolmay not have image content needed to correctly render sections of thepanoramic video that should be visible. Playback may freeze or stalluntil the playback tool can recover by retrieving encoded data andreconstructing panoramic video for the newly visible sections.

SUMMARY

In summary, the detailed description presents innovations in streamconfiguration operations and playback operations for adaptive streamingof panoramic video. In some example implementations, the innovations canhelp avoid disruption in playback of panoramic video if a viewerdramatically changes view direction or zoom factor during playback, orif encoded data for a section of panoramic video is lost (e.g., due tonetwork congestion) or corrupted.

According to one aspect of the innovations described herein, a computersystem implements a panoramic video stream configuration tool thatincludes an input buffer, a formatter, one or more video encoders, andone or more output buffers. The input buffer is configured to store aninput picture of panoramic video. The formatter is configured to createa low-resolution version of the input picture, split the input pictureinto multiple sections according to partition settings, and createmultiple composite pictures. Each of the composite pictures includes oneof the multiple sections and also includes the low-resolution version ofthe input picture. The formatter is configured to add the compositepictures, respectively, to corresponding video streams. The videoencoder(s) are configured to encode the composite pictures in thecorresponding video streams, respectively. This produces encoded datafor the composite pictures as part of multiple bitstreams for thecorresponding video streams, respectively. The output buffer(s) areconfigured to store the encoded data for delivery. In this way, even ifa playback tool retrieves encoded data for only one of the bitstreams,the playback tool has image content (specifically, the low-resolutionversion of the input picture) that it can use to render views of thepanoramic video if the view direction or zoom factor dramaticallychanges, or if encoded data for a specific section is lost or corrupted.The quality of the rendered views (at least for details created from thelow-resolution version of the input picture) may be degradedtemporarily, but playback is not disrupted.

According to another aspect of the innovations described herein, acomputer system implements a panoramic video playback tool that includesa view controller, a streaming controller, one or more input buffers,one or more video decoders, a mapper, and an output buffer. The viewcontroller is configured to determine a view window for playback ofpanoramic video. The view controller is further configured to, fromamong multiple sections of the panoramic video, identify one or moresections that contain at least part of the view window. For theidentified section(s), the view controller is configured to select oneor more bitstreams among multiple bitstreams for corresponding videostreams. The streaming controller is configured to request encoded data,in the selected bitstream(s) for the identified section(s),respectively, for an input picture of the panoramic video. Each of theidentified section(s) is part of a composite picture that also includesa low-resolution version of the input picture. The input buffer(s) areconfigured to store the encoded data. The video decoder(s) areconfigured to decode the encoded data to reconstruct the identifiedsection(s) for the input picture and/or reconstruct the low-resolutionversion of the input picture. The mapper is configured to, based atleast in part on the reconstructed section(s) and/or the reconstructedlow-resolution version of the input picture, create an output picture.Finally, the output buffer is configured to store the output picture foroutput to a display device. Under normal operation, the playback toolcan use the reconstructed section(s) to render high-quality views of thepanoramic video. If the view direction or zoom factor dramaticallychanges, however, or if encoded data for a specific section is lost orcorrupted, the playback tool can use the low-resolution version of theinput picture to render lower-quality details for views of the panoramicvideo, without disruption of playback.

The innovations can be implemented as part of a method, as part of acomputer system configured to perform the method or as part of tangiblecomputer-readable media storing computer-executable instructions forcausing a computer system to perform the method. The various innovationscan be used in combination or separately. This summary is provided tointroduce a selection of concepts in a simplified form that are furtherdescribed below in the detailed description. This summary is notintended to identify key features or essential features of the claimedsubject matter, nor is it intended to be used to limit the scope of theclaimed subject matter. The foregoing and other objects, features, andadvantages of the invention will become more apparent from the followingdetailed description, which proceeds with reference to the accompanyingfigures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example computer system in whichsome described embodiments can be implemented.

FIGS. 2a and 2b are diagrams illustrating example network environmentsin which some described embodiments can be implemented.

FIGS. 3a to 3d are diagrams of example projections for a picture ofpanoramic video, and FIG. 3e is a diagram illustrating an example of ascreen projection for a view of a picture of panoramic video.

FIG. 4 is a diagram illustrating an example architecture for a panoramicvideo stream configuration tool that supports overlapping sections andcomposite pictures.

FIG. 5 is a diagram illustrating an example architecture for a panoramicvideo playback tool that supports overlapping sections and compositepictures.

FIGS. 6a and 6b are diagrams illustrating examples of streamconfiguration operations for adaptive streaming of panoramic video withoverlapping sections.

FIG. 7 is a diagram illustrating an example of overlapping section of apicture of panoramic video in a sinusoidal projection.

FIGS. 8a and 8b are diagrams illustrating examples of playbackoperations for adaptive streaming of panoramic video with overlappingsections.

FIG. 9 is a flowchart illustrating an example technique for streamconfiguration of panoramic video with overlapping sections.

FIG. 10 is a flowchart illustrating an example technique for playback ofpanoramic video with overlapping sections.

FIGS. 11a and 11b are diagrams illustrating examples of streamconfiguration operations for adaptive streaming of panoramic video withcomposite pictures.

FIG. 12 is a diagram illustrating an example composite picture ofpanoramic video.

FIGS. 13a and 13b are diagrams illustrating examples of playbackoperations for adaptive streaming of panoramic video with compositepictures.

FIG. 14 is a flowchart illustrating an example technique for streamconfiguration of panoramic video with composite pictures.

FIG. 15 is a flowchart illustrating an example technique for playback ofpanoramic video with composite pictures.

DETAILED DESCRIPTION

The detailed description presents innovations in stream configurationoperations and playback operations for adaptive streaming of panoramicvideo. The innovations include features of adaptive streaming ofpanoramic video with composite pictures. In some exampleimplementations, the innovations can help avoid disruption in playbackof panoramic video if a viewer dramatically changes view direction orzoom factor during playback, or if encoded data for a section ofpanoramic video is lost (e.g., due to network congestion) or corrupted.The innovations also include features of adaptive streaming of panoramicvideo with overlapping sections. In other example implementations, theinnovations can help avoid disruption in playback of panoramic video asa viewer gradually changes view direction or zoom factor duringplayback.

In the examples described herein, identical reference numbers indifferent figures indicate an identical component, module, or operation.Depending on context, a given component or module may accept a differenttype of information as input and/or produce a different type ofinformation as output.

More generally, various alternatives to the examples described hereinare possible. For example, some of the methods described herein can bealtered by changing the ordering of the method acts described, bysplitting, repeating, or omitting certain method acts, etc. The variousaspects of the disclosed technology can be used in combination orseparately. Some of the innovations described herein address one or moreof the problems noted in the background. Typically, a giventechnique/tool does not solve all such problems.

I. Example Computer Systems

FIG. 1 illustrates a generalized example of a suitable computer system(100) in which several of the described innovations may be implemented.The innovations described herein relate to panoramic video streamconfiguration, streaming, and playback. Aside from its use in panoramicvideo stream configuration, streaming, and/or playback, the computersystem (100) is not intended to suggest any limitation as to scope ofuse or functionality, as the innovations may be implemented in diversecomputer systems, including special-purpose computer systems adapted forpanoramic video stream configuration, streaming, and/or playback.

With reference to FIG. 1, the computer system (100) includes one or moreprocessing cores (110 . . . 11 x) of a central processing unit (“CPU”)and local, on-chip memory (118). The processing core(s) (110 . . . 11 x)execute computer-executable instructions. The number of processingcore(s) (110 . . . 11 x) depends on implementation and can be, forexample, 4 or 8. The local memory (118) may be volatile memory (e.g.,registers, cache, RAM), non-volatile memory (e.g., ROM, EEPROM, flashmemory, etc.), or some combination of the two, accessible by therespective processing core(s) (110 . . . 11 x).

The local memory (118) can store software (180) implementing tools foradaptive panoramic video stream configuration, streaming, and/orplayback, using overlapping sections and/or composite pictures, foroperations performed by the respective processing core(s) (110 . . . 11x), in the form of computer-executable instructions. In FIG. 1, thelocal memory (118) is on-chip memory such as one or more caches, forwhich access operations, transfer operations, etc. with the processingcore(s) (110 . . . 11 x) are fast.

The computer system (100) can include processing cores (not shown) andlocal memory (not shown) of a graphics processing unit (“GPU”). Ingeneral, a GPU is any specialized circuit, different from the CPU, thataccelerates creation and/or manipulation of image data in a graphicspipeline. The GPU can be implemented as part of a dedicated graphicscard (video card), as part of a motherboard, as part of a system on achip (“SoC”), or in some other way (even on the same die as the CPU).The number of processing cores of the GPU depends on implementation. Theprocessing cores of the GPU are, for example, part ofsingle-instruction, multiple data (“SIMD”) units of the GPU. The SIMDwidth n, which depends on implementation, indicates the number ofelements (sometimes called lanes) of a SIMD unit. For example, thenumber of elements (lanes) of a SIMD unit can be 16, 32, 64, or 128 foran extra-wide SIMD architecture. The local memory may be volatile memory(e.g., registers, cache, RAM), non-volatile memory (e.g., ROM, EEPROM,flash memory, etc.), or some combination of the two, accessible by therespective processing cores of the GPU. The processing core(s) of theGPU can execute computer-executable instructions for one or moreinnovations for adaptive panoramic video stream configuration,streaming, and/or playback.

Alternatively, the computer system (100) includes one or more processingcores (not shown) of a system-on-a-chip (“SoC”), application-specificintegrated circuit (“ASIC”) or other integrated circuit, along withassociated memory (not shown). The processing core(s) can executecomputer-executable instructions for one or more innovations foradaptive panoramic video stream configuration, streaming, and/orplayback.

The computer system (100) includes shared memory (120), which may bevolatile memory (e.g., RAM), non-volatile memory (e.g., ROM, EEPROM,flash memory, etc.), or some combination of the two, accessible by theprocessing core(s). Depending on architecture (e.g., whether a GPU ispart of a video card, motherboard, or SoC), CPU memory can be completelyseparate from GPU memory, or CPU memory and GPU memory can, at least inpart, be shared memory or drawn from the same source (e.g., RAM). Thememory (120) stores software (180) implementing tools for adaptivepanoramic video stream configuration, streaming, and/or playback, usingoverlapping sections and/or composite pictures, for operationsperformed, in the form of computer-executable instructions. In FIG. 1,the shared memory (120) is off-chip memory, for which access operations,transfer operations, etc. with the processing cores are slower.

The computer system (100) includes one or more network adapters (140).As used herein, the term network adapter indicates any network interfacecard (“NIC”), network interface, network interface controller, ornetwork interface device. The network adapter(s) (140) enablecommunication over a network to another computing entity (e.g., server,other computer system). The network can be a wide area network, localarea network, storage area network or other network. The networkadapter(s) (140) can support wired connections and/or wirelessconnections, for a wide area network, local area network, storage areanetwork or other network. The network adapter(s) (140) convey data (suchas computer-executable instructions, audio or video input or output, orother data) in a modulated data signal over network connection(s). Amodulated data signal is a signal that has one or more of itscharacteristics set or changed in such a manner as to encode informationin the signal. By way of example, and not limitation, the networkconnections can use an electrical, optical, RF, or other carrier.

The computer system (100) also includes one or more input device(s)(150). The input device(s) may be a touch input device such as akeyboard, mouse, pen, or trackball, a scanning device, or another devicethat provides input to the computer system (100). For video, the inputdevice(s) (150) may be a camera, video card, screen capture module, TVtuner card, or similar device that accepts video input in analog ordigital form, or a CD-ROM or CD-RW that reads video input into thecomputer system (100). The computer system (100) can also include anaudio input, a motion sensor/tracker input, and/or a game controllerinput.

The computer system (100) includes one or more output devices (160). Theoutput device(s) (160) may be a printer, CD-writer, or another devicethat provides output from the computer system (100). For video playback,the output device(s) (160) may be a head-mounted display, computermonitor, or other display device. An audio output can provide audiooutput to one or more speakers.

The storage (170) may be removable or non-removable, and includesmagnetic media (such as magnetic disks, magnetic tapes or cassettes),optical disk media and/or any other media which can be used to storeinformation and which can be accessed within the computer system (100).The storage (170) stores instructions for the software (180)implementing tools for adaptive panoramic video stream configuration,streaming, and/or playback, using overlapping sections and/or compositepictures.

An interconnection mechanism (not shown) such as a bus, controller, ornetwork interconnects the components of the computer system (100).Typically, operating system software (not shown) provides an operatingenvironment for other software executing in the computer system (100),and coordinates activities of the components of the computer system(100).

The computer system (100) of FIG. 1 is a physical computer system. Avirtual machine can include components organized as shown in FIG. 1.

The innovations can be described in the general context ofcomputer-readable media. Computer-readable media are any availabletangible media that can be accessed within a computing environment. Byway of example, and not limitation, with the computer system (100),computer-readable media include memory (118, 120), storage (170), andcombinations thereof. The term computer-readable media does notencompass transitory propagating signals or carrier waves.

The innovations can be described in the general context ofcomputer-executable instructions being executed in a computer system ona target real or virtual processor. The computer-executable instructionscan include instructions executable on processing cores of ageneral-purpose processor to provide functionality described herein,instructions executable to control a GPU or special-purpose hardware toprovide functionality described herein, instructions executable onprocessing cores of a GPU to provide functionality described herein,and/or instructions executable on processing cores of a special-purposeprocessor to provide functionality described herein. In someimplementations, computer-executable instructions can be organized inprogram modules. Generally, program modules include routines, programs,libraries, objects, classes, components, data structures, etc. thatperform particular tasks or implement particular abstract data types.The functionality of the program modules may be combined or splitbetween program modules as desired in various embodiments.Computer-executable instructions for program modules may be executedwithin a local or distributed computer system.

In general, a computer system or device can be local or distributed, andcan include any combination of special-purpose hardware and/or hardwarewith software implementing the functionality described herein. For thesake of presentation, the detailed description uses terms like“determine,” “receive” and “provide” to describe computer operations ina computer system. These terms denote operations performed by a computerand should not be confused with acts performed by a human being. Theactual computer operations corresponding to these terms vary dependingon implementation.

II. Example Network Environments

FIGS. 2a and 2b show example network environments (201, 202) thatinclude video encoders (220) and video decoders (270). The encoders(220) and decoders (270) are connected over a network (250) using anappropriate communication protocol. The network (250) can include theInternet or another computer network.

In the network environment (201) shown in FIG. 2a , each real-timecommunication (“RTC”) tool (210) includes both one or more encoders(220) and one or more decoders (270) for bidirectional communication.Each RTC tool (210) is an example of a panoramic video streamconfiguration tool and a panoramic video playback tool. A given encoder(220) can produce output compliant with the H.265/HEVC standard, ISO/IEC14496-10 standard (also known as H.264/AVC), another standard, or aproprietary format such as VP8 or VP9, or a variation or extensionthereof, with a corresponding decoder (270) accepting and decodingencoded data from the encoder (220). The bidirectional communication canbe part of a video conference, video telephone call, or other two-partyor multi-party communication scenario. Although the network environment(201) in FIG. 2a includes two RTC tools (210), the network environment(201) can instead include three or more RTC tools (210) that participatein multi-party communication.

An RTC tool (210), as a panoramic video stream configuration tool,manages encoding by the encoder(s) (220) and also, as a panoramic videoplayback tool, manages decoding by the decoder(s) (270). FIG. 4 shows anexample panoramic video stream configuration tool (400) that can beimplemented in the RTC tool (210). FIG. 5 shows an example panoramicvideo playback tool (500) that can be implemented in the RTC tool (210).Alternatively, the RTC tool (210) uses another panoramic video streamconfiguration tool and/or another panoramic video playback tool.

In the network environment (202) shown in FIG. 2b , a panoramic videostream configuration tool (212) includes one or more encoders (220) thatencode video for delivery to multiple panoramic video playback tools(214), which include decoders (270). The unidirectional communicationcan be provided for live broadcast video streaming, a video surveillancesystem, web camera monitoring system, remote desktop conferencingpresentation or sharing, wireless screen casting, cloud computing orgaming, or other scenario in which panoramic video is encoded and sentfrom one location to one or more other locations. Although the networkenvironment (202) in FIG. 2b includes two playback tools (214), thenetwork environment (202) can include more or fewer playback tools(214). In general, a playback tool (214) communicates with the streamconfiguration tool (212) to determine one or more streams of video forthe playback tool (214) to receive. The playback tool (214) receives thestream(s), buffers the received encoded data for an appropriate period,and begins decoding and playback.

The stream configuration tool (212) can include server-side controllerlogic for managing connections with one or more playback tools (214). Aplayback tool (214) can include client-side controller logic formanaging connections with the stream configuration tool (212). FIG. 4shows an example panoramic video stream configuration tool (400) thatcan be implemented in the stream configuration tool (212).Alternatively, the stream configuration tool (212) uses anotherpanoramic video stream configuration tool. FIG. 5 shows an examplepanoramic video playback tool (500) that can be implemented in theplayback tool (214). Alternatively, the playback tool (214) uses anotherpanoramic video playback tool.

Alternatively, a Web server or other media server can store encodedvideo for delivery to one or more panoramic video playback tools (214),which include decoders (270). The encoded video can be provided, forexample, for on-demand video streaming, broadcast, or another scenarioin which encoded video is sent from one location to one or more otherlocations. A playback tool (214) can communicate with the media serverto determine one or more streams of video for the playback tool (214) toreceive. The media server can include server-side controller logic formanaging connections with one or more playback tools (214). A playbacktool (214) receives the stream(s), buffers the received encoded data foran appropriate period, and begins decoding and playback.

III. Example Projections for a Picture of Panoramic Video

Panoramic video (sometimes called 360-degree video, immersive video, orspherical video) is video in which views in multiple directions around acentral position are recorded at the same time. A picture of panoramicvideo is a representation of the views in multiple directions recordedat a given time. The picture of panoramic video can include imagecontent in every direction or substantially every direction from thecentral position. More commonly, a picture of panoramic video includesimage content in every direction in a 360-degree circle around thecentral position, including at least some image content above thecentral position and at least some image content underneath the centralview/camera position.

A picture of panoramic video includes sample values, which representcolors at locations of the picture. Depending on how the picture isprojected, sample values of the picture can have various attributes. Ingeneral, sample values can have 8 bits per sample value, 10 bits persample value, 12 bits per sample value, or some other number of bits persample value. The dynamic range of sample values can be standard dynamicrange (e.g., 0 to 100 nits), high dynamic range (e.g., 0 nits to 1000nits, 0 nits to 1500 nits, 0 nits to 4000 nits), or some other dynamicrange. With respect to color gamut, the sample values can have a narrowcolor gamut (common for standard dynamic range video) or a wider colorgamut (common for high dynamic range video), which can potentiallyrepresent colors that are more saturated, or vivid. For a rectilinearprojection, the spatial resolution of a picture of panoramic video canbe 1280×720 sample values (so-called 720p), 1920×1080 sample values(so-called 1080p), 2160×1080 sample values, 3840×2160 (so-called 4K),4320×2160 sample values, 7680×3840 sample values, 7680×4320 samplevalues (so-called 8K), 8640×4320 sample values, or some other number ofsample values per picture. Often, the spatial resolution of a picture ofpanoramic video is very high (e.g., 8K or higher), so as to providesufficient spatial resolution when a smaller view within the picture isrendered. In general, a pixel is the set of one or more collocatedsample values for a location in a picture, which may be arranged indifferent ways for different chroma sampling formats. For a sphericalprojection, spatial resolution can vary.

Typically, before encoding in a rectilinear projection (e.g., anequirectangular projection), sample values of a picture are converted toa color space such as YUV, in which sample values of a luma (Y)component represent brightness or intensity values, and sample values ofchroma (U, V) components represent color-difference values. The precisedefinitions of the color-difference values (and conversion operationsbetween YUV color space and another color space such as RGB) depend onimplementation. In general, as used herein, the term YUV indicates anycolor space with a luma (or luminance) component and one or more chroma(or chrominance) components, including Y′UV, YIQ, Y′IQ and YDbDr as wellas variations such as YCbCr and YCoCg. Chroma sample values may besub-sampled to a lower chroma sampling rate (e.g., for a YUV 4:2:0format) in order to reduce the spatial resolution of chroma samplevalues, or the chroma sample values may have the same resolution as theluma sample values (e.g., for a YUV 4:4:4 format). After decoding,sample values in a rectilinear projection may be converted to anothercolor space, such as an RGB color space. Sample values in a sphericalprojection or screen projection for a picture of panoramic video may bein an RGB color space or other color space.

The image content for a picture of panoramic video can be organized invarious ways. FIG. 3a shows a spherical projection (301) for a pictureof panoramic video. In the spherical projection (301), sample values aremapped to locations equally distant from a central view/camera position.Sample values may be in an RGB color space or other color space close tothe final color space for rendering. The spherical projection (301)provides a conceptually simple way to represent the sample values of thepicture of panoramic video, and may be useful for some modeling andrendering operations. For other stages of processing (e.g., storage,compression, decompression), however, the spherical projection (301) maynot be as efficient as other types of projections.

FIG. 3b shows an equirectangular projection (302) for a picture ofpanoramic video. The equirectangular projection (302) is a usefulrepresentation for storing, compressing, and decompressing sample valuesof the picture of panoramic video. In particular, sample values of theequirectangular projection (302) can be processed with conventionalvideo coding/decoding tools, which process blocks of sample values inrectangular pictures. The equirectangular projection (302) depicts imagecontent in 360 degrees, rotating sideways from a central view/cameraposition, along the horizontal axis that bisects the equirectangularprojection (302); it depicts image content in 180 degrees, rotating upor down from a central view/camera position, along the vertical axis. Inthe equirectangular projection (302), content towards the top of thepicture and content towards the bottom of the picture is stretchedhorizontally, and content midway between the top and bottom is squeezedhorizontally. In addition to causing visible distortion (which is not aproblem to the extent the equirectangular projection (302) is notdirectly rendered for display), the equirectangular projection (302)uses extra sample values to represent the content towards the top of thepicture and content towards the bottom of the picture, which candecrease compression efficiency. Metadata associated with theequirectangular projection (302) can indicate resolution of theequirectangular projection (302) as well as a view direction at each ofone or more locations of the equirectangular projection (302) (e.g.,view direction at the center of the equirectangular projection (302),view direction at the midpoint of the vertical axis along an edge of theequirectangular projection (302)). Or, a default view direction for alocation of the equirectangular projection (302) can be defined. Forexample, the center of the equirectangular projection (302) is definedto be the view direction with pan of zero degrees and pitch of zerodegrees.

FIG. 3c shows a sinusoidal projection (303) for a picture of panoramicvideo. The sinusoidal projection (303) is another useful representationfor storing, compressing, and decompressing sample values of the pictureof panoramic video. A sinusoidal projection is a pseudo-cylindrical,equal-area map projection, in which scale is constant along a centralmeridian (or multiple central meridians), and horizontal scale isconstant throughout the map. A sinusoidal projection can have a singlefold (single central meridian) or multiple folds (multiple centralmeridians) For example, a bi-fold sinusoidal projection can have twocentral meridians of equal length, with the two folds corresponding tohemispheres of the map. Thus, the sinusoidal projection (303) depictsimage content in 360 degrees, rotating sideways from a centralview/camera position, along the horizontal axis that bisects thesinusoidal projection (303); it depicts image content in 180 degrees,rotating up or down from a central view/camera position, along thevertical axis. Unlike the equirectangular projection (302), in thesinusoidal projection (303), content towards the top of the picture andcontent towards the bottom of the picture is not stretched horizontally,and content midway between the top and bottom is not squeezedhorizontally. The sinusoidal projection (303) uses extra sample valueshaving default values (e.g., black, gray) to represent areas outside theactual content, towards the top or bottom of the picture. Although thisapproach results in some sample values not being used to representactual coded panoramic video, compression efficiency still tends to bebetter than with the equirectangular projection (302). Metadataassociated with the sinusoidal projection (303) can indicate resolutionof the sinusoidal projection (303) as well as a view direction at eachof one or more locations of the sinusoidal projection (303) (e.g., viewdirection at the center of the sinusoidal projection (303), viewdirection at the midpoint of the vertical axis along an edge of thesinusoidal projection (303)). Or, a default view direction for alocation of the sinusoidal projection (303) can be defined. For example,the center of the sinusoidal projection (303) is defined to be the viewdirection with pan of zero degrees and pitch of zero degrees.

FIG. 3d shows a cubemap projection (304) for a picture of panoramicvideo. Like the equirectangular projection (302) and sinusoidalprojection (303), the cubemap projection (304) is a usefulrepresentation for storing, compressing, and decompressing sample valuesof the picture of panoramic video, because the faces of the cubemapprojection (304) can be “unfolded” and/or split into separate sectionsfor such operations. In the cubemap projection (304), content towardsthe edges of faces of a cube is stretched horizontally and/orvertically, and content towards the middle of faces is squeezedhorizontally and/or vertically. In general, the extent of suchstretching is less than at the top and bottom of the equirectangularprojection (302), and the cubemap projection (304) may use fewer extrasample values to represent stretched content. Metadata associated withthe cubemap projection (304) can indicate resolution of the cubemapprojection (304) as well as a view direction at each of one or morelocations of the cubemap projection (304). Or, default view directionsfor locations of the cubemap projection (304) can be defined.

During playback, pictures of panoramic video are reconstructed. At leastconceptually, a picture may be represented in spherical projection atthis stage. Typically, a viewer can control a view direction relative tothe central view/camera position for the spherical projection,potentially changing which section of the panoramic video is viewed. Forexample, in addition to specifying heading in degrees or radians fromside to side (i.e., yaw, or pan) for a view direction, the viewer canspecify an inclination in degrees or radians up or down (i.e., pitch, ortilt) for the view direction and even a rotation in degrees or radiansof the view (i.e., roll) for the view direction. Alternatively, the viewdirection can be parameterized in some other way (e.g., as a matrix ofaffine transform coefficients that specify a spatial rotation in threedimensions using Euler angles or quaternion units, corresponding toheading, pitch, and roll values). The viewer may also be able to zoom inor zoom out. A field of view can be specified in degrees (e.g., 90degrees for normal view, 120 degrees for wide view) or radians. When aview of panoramic video is rendered for display, the section of thepanoramic video that is viewed may be projected to a flat image, whichis called a screen projection.

FIG. 3e shows an example of screen projection for a view of a picture ofpanoramic video. An equirectangular projection (302) of the picture isreconstructed, e.g., through video decoding operations and colorconversion operations. The sample values of the picture of panoramicvideo are mapped to the spherical projection (303). In essence, thesample values are projected to the “inside” of the sphere for thespherical projection (303), as viewed from the perspective of aview/camera position at the center of the sphere. Locations in thespherical projection (303) are mapped to corresponding locations in theequirectangular projection (302). If a corresponding location in theequirectangular projection (302) is at or near an integer (whole pixel)offset, the sample value from the corresponding location is assigned tothe location in the spherical projection (303). Otherwise, a samplevalue can be calculated by interpolation between sample values at nearbylocations in the equirectangular projection (302) (e.g., using bilinearinterpolation), and the (interpolated) sample value is assigned to thelocation in the spherical projection (303).

A view window (310) in the spherical projection (303) is found, based ona view direction, zoom factor, and field of view from the centralview/camera position. The view window (310) is projected to a screenprojection (320) for rendering. For example, a perspective transform isapplied to assign sample values to the respective locations of thescreen projection (320) from the sample values of the sphericalprojection (303). For every location of the screen projection (320), asample value is assigned directly from the spherical projection (303) orfrom interpolation between sample values of the spherical projection(303). Thus, the screen projection (320) includes sample values from thespherical projection (303) and, by extension, sample values fromrelevant parts of the equirectangular projection (302).

IV. Examples of Identifying Sections of Pictures in Input Projections

When an application provides a view direction, field of view (if notpre-defined), and zoom factor (if configurable) for rendering a view ofa picture of panoramic video, the application specifies a view window tobe rendered. For example, an application provides an indication of viewdirection to a module of a panoramic video playback tool. The viewdirection can be specified as (1) a heading in degrees or radians fromside to side (i.e., yaw, or pan) from a central view/camera position and(2) an inclination in degrees or radians up or down (i.e., pitch, ortilt) from the view/camera position. The view direction can also include(3) a rotation in degrees or radians of the view (i.e., roll) from theview/camera position. Alternatively, the view direction can beparameterized in some other way (e.g., as a matrix of affine transformcoefficients that specify a spatial rotation in three dimensions usingEuler angles or quaternion units, which correspond to heading, pitch,and roll values). The field of view can be specified in degrees (e.g.,90 degrees for normal view, 120 degrees for wide view) or radians. Azoom factor can be specified as a distance from a view camera position,size of view window, or in some other way. Alternatively, instead ofdirectly providing indications of view direction (and possibly field ofview and zoom factor), an application can specify a source forindications of view direction (and possibly field of view and zoomfactor), in which case the specified source provides the indicationsduring rendering. In any case, the module of the panoramic videoplayback tool finds the appropriate view window for a sphericalprojection of the picture of panoramic video.

The view window typically includes a small proportion of the overallcontent of a picture of panoramic video. To simplify processing and saveresources during operations such as retrieval and decoding of encodeddata, a panoramic video playback tool can identify one or more sectionsof an input picture, in an input projection (such as an equirectangularprojection, cubemap projection, sinusoidal projection, or otherprojection), that contain the view window, then use that information tolimit which operations are performed when reconstructing the picture ofpanoramic video. In particular, the panoramic video playback tool canlimit operations to the identified section(s) of the picture in theinput projection.

For example, a panoramic video playback tool finds a view window of aspherical projection based on a view direction (and field of view andzoom factor, which may be pre-defined). Based on the view window, theplayback tool identifies one or more sections of an input picture (in aninput projection such as an equirectangular projection, cubemapprojection, or sinusoidal projection) that contain the view window ofthe spherical projection. Given a view window of the sphericalprojection, the playback tool can project from the spherical projectionback to the input projection to identify a corresponding window in theinput picture of panoramic video, then identify those sections in theinput picture that include any part of the corresponding window. Thecorresponding window in the input picture can have an irregular boundaryand be split (e.g., across an edge). In this way, the playback tool canidentify any section of the picture that contains at least part of theview window.

Typically, the identified section(s) are aligned with boundaries ofgroups of sample values (e.g., blocks, slices, tiles) for differentoperations in the reconstruction process. Depending on the position andsize of the view window, one section of the picture may include theentire view window. Or, multiple sections of the picture maycollectively include the view window. The multiple sections can becontiguous or, if the view window crosses an edge of the picture, benon-contiguous. The playback tool can limit operations (such asretrieval of encoded data, decoding of encoded data, and creation ofoutput pictures) to the identified section(s).

V. Example Architectures for Adaptive Streaming of Panoramic Video

When a panoramic video stream configuration tool receives input picturesof panoramic video, the stream configuration tool produces encoded datafor the panoramic video in multiple bitstreams. When a panoramic videoplayback tool receives encoded data for panoramic video, the playbacktool renders views of the panoramic video. This section describesvarious aspects of example architectures for stream configuration andexample architectures for playback of panoramic video, including use ofoverlapping sections and composite pictures.

Panoramic video can be produced and streamed for various use casescenarios. For example, panoramic video can be produced and streamed fora live event such as a concert or sporting event. Or, as anotherexample, panoramic video can be produced and streamed for an immersiveexperience for education, virtual travel, or a virtual walk-through fora real estate listing. Or, as another example, panoramic video can beproduced and streamed for conferencing or tele-medicine. Or, as anotherexample, panoramic video can be produced and streamed for immersivegameplay broadcasting.

Panoramic video can be played back in various ways. For example,panoramic video can be played back through a Web browser or videoplayback application, executing on a game console, desktop computer, orother computing platform. Or, as another example, panoramic video can beplayed back through a mobile device or head-mounted display for a VR orAR application.

In some configurations, a single entity manages end-to-end behavior of apanoramic video stream configuration tool and one or more panoramicvideo playback tools. In such configurations, the stream configurationtool and playback tool(s) can exchange information about partitioning ofinput pictures into sections, organization of composite pictures, streamselection decisions, etc. in one or more private channels. Inalternative configurations, the panoramic video stream configurationtool and panoramic video playback tool(s) are managed by differententities. In such configurations, the stream configuration tool andplayback tool(s) can interoperate across standardized interfaces,according to defined protocols, to exchange information aboutpartitioning of input pictures into sections, organization of compositepictures, stream selection decisions, etc.

A. Example Stream Configuration Architectures

FIG. 4 shows an example architecture for a panoramic video streamconfiguration tool (400) that supports overlapping sections andcomposite pictures. In addition to a video source (410) and a mediaserver (490), the example architecture includes a panoramic video streamconfiguration tool (400) with an input buffer (430), a formatter (440),one or more video encoders (460), and one or more output buffers (470).

The video source (410) provides input pictures (420) of panoramic videoto the input buffer (430). For example, the video source (410) includesa buffer associated with an omnidirectional camera, which produces inputpictures (420) of panoramic video. Alternatively, the video source (410)includes buffers associated with a collection of cameras, which producepictures taken in different directions at a location, and a buffer thatstores input pictures (420) of panoramic video aggregated, mosaicked,composited, etc. from the pictures produced by the cameras. The camerascan be physical cameras that record natural video or virtual camerasthat record video in a synthetic environment (e.g., game environment).Alternatively, the stream configuration tool (400) can itself create theinput pictures (420) of panoramic video, which are stored in the inputbuffer (430), from pictures of streams that the stream configurationtool (400) receives. The panoramic video stream configuration tool (400)can implemented at a content production site, co-located with the videosource (410) or cameras. Alternatively, the panoramic video streamconfiguration tool (400) can be implemented at a remote site (e.g., Webserver), with the video source (410) providing input pictures (420) ofpanoramic video to the configuration tool (400) over a network, orcameras providing streams of video to the configuration tool (400) overa network.

The input buffer (430) is configured to receive and store one or moreinput pictures (420) of panoramic video. Typically, an input picture(420) is in an input projection. For example, the input projection canbe an equirectangular projection, cubemap projection, sinusoidalprojection, or other type of projection. In some exampleimplementations, an input picture (420) has a spatial resolution of 4Kor higher. Alternatively, an input picture (420) can have a lowerspatial resolution.

The formatter (440) is configured to split each input picture (420) intomultiple sections (445) (n sections) according to partition settings.The value of n depends on implementation. For example, n is 6, 8, 12, or16. A data store (not shown) can store various settings for thepanoramic video stream configuration tool (400). For example, thesettings can include partition settings used to split input pictures(420) of panoramic video into sections (445). The partition settings caninclude the count n of sections (445) into which input pictures (420)are partitioned, the relative sizes and positions of the sections (445),and (for overlapping sections) the extent of overlap between sections(445). The spatial resolution of the sections (445) depends onimplementation. In some example implementations, the sections (445) eachhave a spatial resolution of 1080p, 720p, or some other resolution thatis readily accepted by the video encoder(s) (460) and large enough tocontain the content for a typical view window in playback, but smallenough to exclude content of the panoramic video outside of a typicalview window (to avoid unnecessary retrieval and reconstruction ofcontent during playback).

In some configurations, the n sections (445) are non-overlapping. Inother configurations, the n sections (445) are overlapping. That is,each of the n sections (445) overlaps at least one other section amongthe n sections (445). In some example implementations, each of the nsections (445) overlaps each adjacent section among the n sections. Theoverlapping of the sections (445) tends to decrease overall compressionefficiency (because the same sample values may be redundantly encoded indifferent sections). On the other hand, the overlapping of the sections(445) tends to reduce the incidence of disruption of playback caused bybitstream switching. The formatter (440) is configured to add the nsections (445) to corresponding video streams. In FIG. 4, there are nstreams for the n sections (445), which are labeled 0 . . . n−1.

The formatter (440) can be configured to project the input picture (420)from an input projection to an intermediate projection, such that the nsections (445) are in the intermediate projection. For example, theinput projection is an equirectangular projection or a cubemapprojection, and the intermediate projection is a sinusoidal projection.In this case, at least one of the n sections (445) includes at leastsome sample values having default values, not representing content ofthe input picture of panoramic video.

The formatter (440) can be configured to receive an indication offeedback and, based at least in part on the indication of feedback,adjust the partition settings. For example, the indication of feedbackincludes an indication of network connection quality, an indication ofmagnitude of view window change activity, an indication of which viewdirection is prevalent, and/or some other type of feedback. To adjustthe partition settings, the formatter (440) can be configured to changean extent of overlap between overlapping sections, change a count of then sections (445), change relative sizes of at least some of the nsections (445), change positions of at least some of the n sections(445), add one or more sections, at new positions, to the n sections(445), remove one or more sections from the n sections (445), and/ormake some other change to the partition settings.

In some configurations, the formatter (440) is configured to create alow-resolution version of the input picture (420). For example, theformatter (440) downsamples the input picture (420) horizontally and/orvertically. The low-resolution version of the input picture (420) canhave a width the same as one of the n sections (e.g., 1920 sample valuesfor a 1080p section, 1280 sample values for a 720p section). The heightof the input picture (420) can be reduced proportionally. The formatter(440) is further configured to, after splitting the input picture (420)into n sections (445) (which can be overlapping or non-overlapping,depending on implementation) according to partition settings, create ncomposite pictures (446). Each of the n composite pictures (446)includes one of the n sections (445) and also includes thelow-resolution version of the input picture (420). The formatter (440)is configured to add the n composite pictures (446), including the nsections (445), respectively, to corresponding video streams.

A composite picture (446) can be organized in various ways. For example,for each of the n composite pictures (446), the low-resolution versionof the input picture (420) is adjacent one of the n sections (445)within the composite picture (446). Or, as another example, for each ofthe n composite pictures (446), one of the n sections (445) provides afirst view of a frame packing arrangement, and the low-resolutionversion of the input picture (420) provides a second view of the framepacking arrangement. Within a composite picture (446), thelow-resolution version of the input picture (420) can be positioned at apre-defined location relative to one of the n sections (445).Alternatively, within a composite picture (446), the low-resolutionversion of the input picture (420) can be positioned at a variablelocation relative to one of the n sections (445).

The input picture (420) and the low-resolution version of the inputpicture (420) can be in an input projection, such as an equirectangularprojection or a cubemap projection. The formatter (440) can be furtherconfigured to project the input picture (420) from the input projectionto an intermediate projection, such as a sinusoidal projection. In acomposite picture (446), the low-resolution version of the input picture(420) can be in the input projection or the intermediate projection.

The video encoder(s) (460) are configured to encode sample values of then sections (445) or n composite pictures (446) in the correspondingvideo streams, respectively. The sample values are, for example, 8-bitsample values or 10-bit sample values in a YUV color space, with achroma sampling rate of 4:2:0. Alternatively, the sample values encodedby the video encoder(s) (460) are in another format. The encodingproduces encoded data (465) for the n sections (445) or n compositepictures (446) as part of n bitstreams for the corresponding videostreams, respectively. For example, the n bitstreams are videoelementary bitstreams. Depending on implementation and the format of theencoded data, the video encoder(s) (460) can produce encoded dataconformant to the H.265/HEVC standard, ISO/IEC 14496-10 standard (alsoknown as H.264/AVC), another standard, or a proprietary format such asVP8 or VP9, or a variation or extension thereof. The streamconfiguration tool (400) can include a multiplexer (not shown)configured to combine the encoded data, for the n bitstreams, into asingle container stream.

The formatter (440) is further configured to produce one or moremanifest files (442). The manifest file(s) (442) include informationindicating, for each of the n bitstreams, the position (e.g., incoordinates of the input picture (420), or in coordinates of a sphericalprojection) of one of the n sections (445) whose content is part of thecorresponding video stream for that bitstream. The manifest file(s)(442) can also include information that indicates where thelow-resolution version of the input picture (420) is positioned in the ncomposite pictures (446), respectively.

The output buffer(s) (470) are configured to store the encoded data(465) for delivery to the media server (490). The output buffer(s) canalso store the manifest file(s) (442) for delivery to the media server(490). The media server (490) can be a Web server or other server,connected over a network, that stores encoded data (465) for the nstreams of sections (or composite pictures) of the panoramic video andstreams the encoded data (465) for selected bitstreams to playback toolsfor playback.

Depending on implementation and the type of processing desired, modulesof the panoramic video stream configuration tool (400) can be added,omitted, split into multiple modules, combined with other modules,and/or replaced with like modules. In alternative embodiments, panoramicvideo stream configuration tools with different modules and/or otherconfigurations of modules perform one or more of the describedtechniques. Specific embodiments of panoramic video stream configurationtools typically use a variation or supplemented version of the panoramicvideo stream configuration tool (400). The relationships shown betweenmodules within the panoramic video stream configuration tool (400)indicate general flows of information in the panoramic video streamconfiguration tool (400); other relationships are not shown for the sakeof simplicity.

In general, a given module of the panoramic video stream configurationtool (400) can be implemented by software executable on a CPU, bysoftware controlling special-purpose hardware (e.g., a GPU or othergraphics hardware for video acceleration), or by special-purposehardware (e.g., in an ASIC). In particular, in some exampleimplementations, video encoding operations and re-projection operationsto map sample values between different projections are implemented withshader instructions executable on a GPU. Thus,computationally-intensive, repetitive operations (e.g., for videoencoding, for mapping between different types of projections whensplitting input pictures into sections) are likely to be implementedwith graphics hardware (e.g., as shader instructions for a GPU) or otherspecial-purpose hardware, and higher-level operations (e.g., decidinghow to partition input pictures) are likely to be implemented insoftware executable on a CPU.

B. Example Playback Architectures

FIG. 5 shows an example architecture for a panoramic video playback tool(500) that supports overlapping sections and composite pictures. Inaddition to a media server (530), application (580), and display device(590), the example architecture includes a panoramic video playback tool(500) with a view controller (510), a streaming controller (520), one ormore input buffers (540), one or more video decoders (550), a mapper(570), and one or more output buffers (585).

The application (580) can be provided by a third party or packaged aspart of the panoramic video playback tool (500). The application (580)can separated from other modules of the panoramic video playback tool(500) (system-provided modules) by an application programming interface(“API”).

A data store (not shown) can store various settings for the panoramicvideo playback tool (500). For example, the settings can includeinformation provided by the application (580) when the application (580)is installed. Other modules can interact with the data store across aninterface.

The view controller (510) is configured to determine a view window forplayback of panoramic video. For example, the view window depends on aview direction. The view controller (510) is configured to receive anindication of a view direction (582) for the application (580). In FIG.5, the application (580) provides the indication of the view direction(582). Instead of the application (580), another source (e.g., a sourcebased on one or more sensors such as one or more accelerometers,gyroscopes, tilt sensors, optical sensors, cameras, etc., or a source ofuser input events for key presses, mouse cursor movements, mouse scrollwheel movements, remote control input, game controller input, touchscreen input, etc.) can provide the indication of the view direction(582). For example, the view direction (582) is parameterized asdescribed in section IV. The view window can also depend on a field ofview and/or zoom factor. In some configurations, the view controller(510) is also configured to receive an indication of a field of view(584) for the application (580), from the application (580) or anothersource. For example, the field of view (584) is parameterized asdescribed in section IV. The field of view (584) can be defined for theapplication (580) or for a playback session. In some configurations, theview controller (510) is also configured to receive an indication of azoom factor for the application (580), from the application (580) oranother source. For example, the zoom factor is parameterized asdescribed in section IV. Typically, the zoom factor can changedynamically (e.g., to zoom in or zoom out) during a playback session.

The view controller (510) is configured to receive one or more manifestfiles (542) and use the manifest file(s) (542) to identify one or moresections that contain at least part of the view window and/or select oneor more bitstreams for the identified section(s). The manifest file(s)(542) are provided from an input buffer (540), which can receive themanifest file(s) (542) from the media server (530) or directly from astream configuration tool. The manifest file(s) (542) includeinformation indicating, for each of n bitstreams, the position (e.g., incoordinates of the input picture (420), or in coordinates of a sphericalprojection) of one of n sections whose content is part of thecorresponding video stream. The manifest file(s) (542) can also includeinformation that indicates where the low-resolution version of an inputpicture is positioned in composite pictures (556), respectively.

The view controller (510) is also configured to, from among multiplesections (n sections) of the panoramic video, identify one or moresections that contain at least part of the view window. For example, theview controller (510) is configured to identify each of the n sectionsthat contains at least part of the view window. The view controller(510) can identify the section(s) that each contain at least part of theview window as described in section IV. Or, the view controller (510)can simply use position information (e.g., coordinates of a sphericalprojection) in the manifest file(s) (542) to identify the section(s)that each contain at least part of the view window. The identifiedsection(s) can be contiguous sections for an input picture in an inputprojection (e.g., equirectangular projection, cubemap projection,sinusoidal projection). Or, the identified section(s) can benon-contiguous sections that wrap around one or more edges of an inputpicture in an input projection. The view controller (510) is furtherconfigured to, for the identified section(s), select one or morebitstreams among n bitstreams for corresponding video streams. The viewcontroller (510) is configured to pass a control signal (512) to thestreaming controller (520) that indicates the selected bitstream(s). Inthis way, the view controller (510) can iteratively perform operationsto determine the view window, identify the section(s) that contain atleast part of the view window, and select the bitstream(s) for theidentified section(s).

In some configurations, the n sections are non-overlapping. In otherconfigurations, the n sections are overlapping. That is, each of the nsections overlaps at least one other section among the n sections. Insome example implementations, each of the n sections overlaps eachadjacent section among the n sections. The overlapping of the n sectionstends to decrease overall compression efficiency (because the samesample values may be redundantly encoded in different sections). On theother hand, the overlapping of the n sections also tends to reduce theincidence of playback disruption attributable to bitstream switching. Inparticular, when there is gradual panning motion out of a section orzooming to a new section, the overlapping of the n sections gives a wayto render high-resolution views quickly and without playback disruption.Although the playback tool (500) can switch to a new bitstream for a newsection, stream switching can take time (e.g., to send the request forthe new bitstream to the media server (530), and to wait for a switchpoint at which decoding can begin in the new bitstream). For example,stream switching can take 3-5 seconds. With overlapping sections, if theview direction and/or zoom factor changes, the view controller (510) canidentify new sections/streams that are to be used to create an outputpicture (575) for the view window sooner. Because of overlap betweenadjacent sections, for changes in view direction and/or zoom factor thatare gradual and consistent, the view controller (510) in effectpre-fetches a new section as the view window moves out of a currentsection into the new section. By the time the view window reaches anon-overlapping part of the adjacent, new section, content for theadjacent, new section has already been retrieved and reconstructed,assuming the motion of the view window is not extreme. This hidesnetwork latency and stream switching latency from the viewer, anddisruption of playback is avoided.

The view controller (510) can be configured to send an indication offeedback (e.g., to a stream configuration tool or to an aggregator forfeedback). The feedback can then be used to adjust the partitionsettings applied when splitting an input picture into sections. Forexample, the indication of feedback includes an indication of networkconnection quality, an indication of magnitude of view window changeactivity, an indication of which view direction is prevalent, and/oranother type of feedback.

The view controller (510) is configured to provide an indication (515)of the identified section(s) to the mapper (570). The mapper (570) canuse the indication (515) of the identified section(s), as well as themanifest file(s) (542), when creating an output picture (575) for theview window.

The streaming controller (520) is configured to request encoded data, inthe selected bitstream(s) for the identified section(s), respectively,for an input picture of the panoramic video. Depending on configuration,the streaming controller (520) can send a request (522) for encoded data(532) to the media server (530), directly to a panoramic video streamconfiguration tool, or to a local media store (531). The streamingcontroller (520) can make separate requests (522) for encoded data (532)for different portions (e.g., slices, tiles) of an input picture or foreach input picture, or it can batch requests.

The media server (530) can be a Web server or other server, connectedover a network, that is configured to store encoded data (532) for the nbitstreams for sections of the panoramic video, and stream the encodeddata (532) for selected ones of the n bitstreams to playback tools forplayback. In the scenario shown in FIG. 5, the media server (530)streams encoded data (532) for one or more selected bitstreams, whichcorrespond to the identified sections(s) that contain a view window forplayback.

If a media server (530) is not used, the panoramic video playback tool(500) can retrieve encoded data (532) for the selected bitstream(s) froma media store (531). The media store (531) can be a magnetic disk,optical storage media, non-volatile memory, or other storage or memory,connected locally to the panoramic video playback tool (500), that isconfigured to store encoded data (532) for panoramic video, and provideit for playback.

In some configurations, each of the identified section(s) is part of acomposite picture (556) that also includes a low-resolution version ofthe input picture. The low-resolution version typically results fromdownsampling the input picture horizontally and/or vertically. Thelow-resolution version of the input picture can have a width the same asone of the n sections (e.g., 1920 sample values for a 1080p section,1280 sample values for a 720p section), with the height of the inputpicture reduced proportionally.

A composite picture (556) can be organized in various ways. For example,for each of n composite pictures (556), the low-resolution version ofthe input picture is adjacent one of the n sections within the compositepicture (556). Or, as another example, for each of n composite pictures(556), one of the n sections (555) provides a first view of a framepacking arrangement, and the low-resolution version of the input pictureprovides a second view of the frame packing arrangement. Within acomposite picture (556), the low-resolution version of the input picturecan be positioned at a pre-defined location relative to one of the nsections (555). Alternatively, within a composite picture (556), thelow-resolution version of the input picture can be positioned at avariable location relative to one of the n sections (555).

The input buffer(s) (540) are configured to store the encoded data (532)for the selected bitstream(s). One of the input buffer(s) can also storethe manifest file(s) (542), which may be provided by the media server(530), local media store (531), or a stream configuration tool. Theinput buffer(s) (540) are configured to provide encoded data (532) forselected bitstreams(s) to the video decoder(s) (550).

The video decoder(s) (550) are configured to decode the encoded data(532) to reconstruct the identified section(s) for the input picture,producing sample values for one or more reconstructed sections (555)from the corresponding video streams. When the selected bitstream(s)include composite picture(s) (556), the video decoder(s) are alsoconfigured to decode the encoded data (532) for the low-resolutionversion of the input picture, producing sample values for thelow-resolution version of the input picture. Depending on implementationand the format of the encoded data, the video decoder(s) (550) candecode the encoded data (532) in a manner consistent with the H.265/HEVCstandard, ISO/IEC 14496-10 standard (also known as H.264/AVC), anotherstandard, or a proprietary format such as VP8 or VP9, or a variation orextension thereof. The sample values are, for example, 8-bit samplevalues or 10-bit sample values in a YUV color space, with a chromasampling rate of 4:2:0. Alternatively, the sample values output by thevideo decoder(s) (550) are in another format.

The mapper (570) is configured to, based at least in part on thereconstructed section(s) (555) and/or the reconstructed low-resolutionversion of the input picture from the composite picture(s) (556), createan output picture (575). For example, the mapper (570) is configured touse the indication (515) of the identified section(s), as well as themanifest file(s) (542), to determine which sample values of thereconstructed section(s) (555), respectively, to map to the outputpicture (575). The mapper (570) can be configured to determine whichsample values of the output picture (575) cannot be determined using thereconstructed section(s) (555) and, for any sample value of the outputpicture (575) that cannot be determined using the reconstructedsection(s) (555), determine that sample value of the output picture(575) using the reconstructed low-resolution version of the inputpicture. Thus, the output picture (575) can be created using only samplevalues of the reconstructed section(s) (555). Or, the output picture(575) can be created using only sample values of the reconstructedlow-resolution version of the input picture. Or, at least part of theoutput picture (575) can be created using sample values of thereconstructed section(s) (555), and at least part of the output picture(575) can be created using sample values of the reconstructedlow-resolution version of the input picture.

In general, the mapper (570) is configured to perform various colorspace conversion operations, chroma rate upsampling operations,projection operations, interpolation operations, and spatial upsamplingoperations. For example, the mapper (570) is configured to convert atleast some of the sample values produced by the video decoder(s) (550)from a first color space (such as a YUV color space) to a second colorspace (such as an RGB color space). The mapper (570) can be configuredto, before color space conversion or as part of color space conversion,perform chroma sample rate upsampling, to restore chroma sample valuesto have the same resolution as luma sample values in the decoded video.To create the output picture (575), the mapper (570) can be configuredto project the reconstructed section(s) (555) from an intermediateprojection (e.g., a sinusoidal projection) to an output projection(e.g., a screen projection). To create the output picture (575), themapper (570) can also be configured to project the reconstructedlow-resolution version of the input picture from an input projection(e.g., equirectangular projection, cubemap projection) or intermediateprojection (e.g., a sinusoidal projection) to an output projection(e.g., a screen projection). The mapper (570) is configured to determineappropriate sample values of the output picture (575) from sample valuesat corresponding locations in the reconstructed section(s) (555) orreconstructed low-resolution version of the input picture, potentiallyselecting sample values at the corresponding locations or performinginterpolation operations (e.g., bilinear interpolation operations) todetermine sample values at the corresponding locations between adjacentsample values of the reconstructed section(s) (555) or reconstructedlow-resolution version of the input picture. The mapper (570) can beconfigured to perform spatial upsampling operations on sample values ofthe reconstructed low-resolution version of the input picture, toreverse downsampling operations performed when creating thelow-resolution version of the input picture.

The output buffer(s) (585) are configured to store the output picture(575) for output to a display device (590). The display device (590) canbe a head-mounted display, computer monitor, television screen, mobiledevice screen, or other type of display device.

In some example implementations, for a platform rendering mode, themapper (570) provides the output picture (575) in a screen projection(586) to the application (580), e.g., to an output buffer (585)indicated by the application (580) for rendering. The application (580)can be a lightweight application that does not itself perform renderingoperations for panoramic video, which simplifies implementation for theapplication (580). For example, the application (580) is a news viewer,real estate site listing application, or other application that does notspecialize in presentation of panoramic video. Instead, the application(580) provides a view direction (582) and may also provide a field ofview (584), and the “platform” (system-provided modules of the playbacktool (500)) performs operations to generate a screen projection.Alternatively, the application (580) can set a source for view direction(582) and field of view (584), and the platform gets the view direction(582) and field of view (584) information from that source. Theapplication (580) may also have an on/off control for rendering.

In other example implementations, in an application rendering mode, themapper (570) provides the output picture (575) in a flat projection tothe application (580), e.g., to an output buffer (585) indicated by theapplication (580). The flat projection can be an equirectangularprojection or a cubemap projection, which may be re-projected so that itis centered at the view window, may have irrelevant details croppedaway, and/or may have its spatial resolution enhanced for relevantdetails. In application rendering mode, the application (580) includes amodule that performs additional transformations to the sample values ofthe output picture (575) in the flat projection (e.g., mapping tospherical projection, mapping to screen projection) so as to generateone or more screen projections appropriate for the application (580),which gives the application (580) more control over rendering decisions.For example, the application (580) is a VR application, AR application,or specialty media application for panoramic video. In applicationrendering mode, different applications can use different approaches torendering of flat projections. For a mobile device or computer monitor,a single screen projection may be rendered. Or, for a head-mounteddisplay (or mobile device held in a head-mounted band), an application(580) may generate two screen projections, for the left and right eyes,respectively.

The streaming controller (520) can selectively retrieve encoded data foradditional bitstream(s). For example, if playback of panoramic video ispaused, the streaming controller (520) can request encoded data for therest of an input picture, and the video decoder(s) (550) can decode therest of the input picture. In this way, the entire input picture isavailable for rendering should the viewer choose to navigate through the“paused” environment of the panoramic video.

Depending on implementation and the type of processing desired, modulesof the panoramic video playback tool (500) can be added, omitted, splitinto multiple modules, combined with other modules, and/or replaced withlike modules. For example, although shown separately in FIG. 5, the viewcontroller (510) can be combined with the mapper (570) (i.e., part ofthe mapper (570)), or the view controller (510) can be combined with thestreaming controller (520) (i.e., part of the streaming controller(520)). In alternative embodiments, panoramic video playback tools withdifferent modules and/or other configurations of modules perform one ormore of the described techniques. Specific embodiments of panoramicvideo playback tools typically use a variation or supplemented versionof the panoramic video playback tool (500). The relationships shownbetween modules within the panoramic video playback tool (500) indicategeneral flows of information in the panoramic video playback tool (500);other relationships are not shown for the sake of simplicity.

In general, a given module of the panoramic video playback tool (500)can be implemented by software executable on a CPU, by softwarecontrolling special-purpose hardware (e.g., a GPU or other graphicshardware for video acceleration), or by special-purpose hardware (e.g.,in an ASIC). In particular, in some example implementations, videodecoding operations and re-projection operations to map sample valuesbetween different projections are implemented with shader instructionsexecutable on a GPU. Thus, computationally-intensive, repetitiveoperations (e.g., for video decoding, for mapping between differenttypes of projections when creating an output picture) are likely to beimplemented with graphics hardware (e.g., as shader instructions for aGPU) or other special-purpose hardware, and higher-level operations(e.g., selecting which streams to request) are likely to be implementedin software executable on a CPU.

VI. Examples of Panoramic Video Streaming with Overlapping Sections

This section describes examples of panoramic video streaming withoverlapping sections. Some examples relate to stream configurationoperations, and other examples relate to playback operations.

Partitioning pictures of panoramic video into overlapping sections candecrease overall compression efficiency, because the same sample values(for overlap regions) are encoded separately in different sections. Thatis, more bits are used for encoded data for the overlapping sections,collectively.

On the other hand, partitioning pictures of panoramic video intooverlapping sections also tends to reduce the incidence of playbackdisruption attributable to bitstream switching. For example, whengradual panning motion or zooming causes a view window to no longeroverlap a section, the overlapping can allow a playback tool to renderhigh-resolution views quickly and without playback disruption. Switchingto a new bitstream for a new section can take time (e.g., to send therequest for the new bitstream to a media server, and to wait for aswitch point at which decoding can begin in the new bitstream). Withoverlapping sections, if the view direction and/or zoom factor changes,the playback tool can more quickly identify new sections/streams thatare to be used to create an output picture for the view window. Becauseof overlap between adjacent sections, for changes in view directionand/or zoom factor that are gradual and consistent, the playback tool ineffect preemptively fetches encoded data for a new section as the viewwindow moves out of a current section into the new section. By the timethe view window reaches a non-overlapping part of the adjacent, newsection, content for the adjacent, new section has already beenretrieved and reconstructed, assuming the motion of the view window isnot extreme. This hides network latency and stream switching latencyfrom the viewer, and disruption of playback is avoided. Thus, usingoverlapping sections can facilitate local responsiveness where there aregradual changes in view direction or zoom during playback. Usingoverlapping sections provides for some “cushion” if a view windowsuddenly changes position within sections whose content has beenretrieved and reconstructed.

A. First Example of Stream Configuration Operations for AdaptiveStreaming of Panoramic Video with Overlapping Sections

FIG. 6a shows a first example (601) of stream configuration operationsfor adaptive streaming of panoramic video with overlapping sections. Inthe first example (601), an input picture (610) of panoramic video is inan equirectangular projection.

With reference to FIG. 6a , a stream configuration tool receives orcreates a series of input pictures—such as the input picture (610)—in anequirectangular projection. The input pictures can be created frommultiple camera video streams (associated with different views from acentral position) or from a video stream from an omnidirectional camera.For example, the resolution of the input pictures in the equirectangularprojection is 4K (3840×2160) or higher.

For different values of phi (φ) and theta (θ) in spherical projectioncoordinates, the stream configuration tool splits the input picture(610) into overlapping sections (630). In general, the overlappingsections (630) are associated with different view directions. Each ofthe overlapping sections (630) corresponds to a region of the surface ofthe sphere for the panoramic video, and is parameterized using a rangeof phi and theta coordinates for the surface of the sphere.Alternatively, the sections (630) can be parameterized in some otherway.

The overlapping sections (630) can have the same size or differentsizes. For example, each of the overlapping sections (630) has a spatialresolution of 1080p, 720p, or some other size. Collectively, theoverlapping sections (630) cover all of the actual content of the inputpicture (610). In FIG. 6a , the input picture (610) is partitioned intosix overlapping sections. More generally, the number n of sectionsdepends on implementation (e.g., n is 8, 12, 16, or 32). Each of theoverlapping sections (630) overlaps with neighboring sections of theinput picture (610). The extent of overlap depends on implementation(e.g., 10%, 20%, 30%). In general, having more extensive overlapprovides more “lead time” for retrieval of encoded data for adjacentsections when view direction, field of view, or zoom factor changesduring playback. On the other hand, having more extensive overlapresults in redundant encoding of more sample values, which can increaseoverall bit rate and increase the bit rate per stream (section).

The extent of overlap can be static. For example, by default, the inputpicture (610) is always partitioned in the same way (or in a way thatdepends on resolution of the input picture (610), picture size for thevideo streams to be encoded, extent of overlap, or other factors knownat the start of stream configuration). Alternatively, the count ofoverlapping sections (630), sizes of overlapping sections (630), andextent of overlap can be configurable and/or adjustable during streamconfiguration and playback. In particular, the extent of overlap can beadjusted depending on factors such as the expected reliability of anetwork connection and how much the position of a view window isexpected to change (e.g., due to panning or zooming). If a networkconnection is reliable, less overlap is needed to hide latency problemsfor stream switching events. If a network connection is unreliable, moreoverlap is needed to hide latency problems for stream switching events.If the position of a view window is expected to be stationary, lessoverlap is needed to hide latency problems for stream switching events.If the position of a view window is expected to change quickly, moreoverlap is needed to hide latency problems for stream switching events.

Different variations of partitioning can be applied that have differentextents of overlap. For example, resources permitting, one version ofoverlapping sections (630) can have less overlap (e.g., 5%) and be usedfor playback tools that have view windows that are relatively stationaryand connect over reliable network connections. Another version ofsections can have more overlap (e.g., 30%) and be used for playbacktools that have view windows that change position quickly and/or areconnect over unreliable network connections.

The stream configuration tool can generate as many phi/thetacombinations as desired for the overlapping sections (630). Thesecombinations can be preset or adapted to a requested view. For example,the “center” of the partitioning pattern can change, based on where thefocus (or expected focus) of most view windows will be. If there is asection/stream centered at the focus, a playback tool might not need torequest and combine sections from multiple bitstreams. Alternatively, anew section could simply be added, centered at the focus.

The stream configuration tool also creates a manifest file (not shown)that indicates the spherical coordinates associated with the respectiveoverlapping sections (630). Alternatively, parameters can be sent insome other way for each of the overlapping sections (630), indicatingwhat part of the input picture (610) is covered by that section. Theparameters can be values of phi and theta per section or otherinformation used to derive the same information about the scope of thesection.

The stream configuration tool adds the overlapping sections (630) tocorresponding video streams. In FIG. 6a , the six overlapping sections(630) are added to corresponding video streams (650 . . . 655),respectively.

The stream configuration tool encodes the corresponding video streams(650 . . . 655), respectively, producing bitstreams of encoded data (670. . . 675) for the respective sections. Thus, the stream configurationtool encodes the multiple overlapping sections (630) partitioned fromthe input picture (610) as part of different video streams (650 . . .655). Section 1 is encoded as a picture of stream 1, section 2 isencoded as a picture of stream 2, and so on. In this way, differentsections of the input picture (610) of panoramic video are representedin different bitstreams of encoded data (670 . . . 675).

Finally, the stream configuration tool buffers the encoded data (670 . .. 675). The encoded data (670 . . . 675) can be directly sent to one ormore playback tools. In most configurations, however, the encoded data(670 . . . 675) is sent to a media server. The media server can alsostore a manifest file with details about the overlapping sections (630)and streams.

B. Second Example of Stream Configuration Operations for AdaptiveStreaming of Panoramic Video with Overlapping Sections

FIG. 6b shows a second example (602) of stream configuration operationsfor adaptive streaming of panoramic video with overlapping sections. Inthe second example (602), the input picture (612) is in a sinusoidalprojection.

With reference to FIG. 6b , the stream configuration tool receives orcreates a series of input pictures—such as the input picture (612)—in asinusoidal projection. From an input picture in an equirectangularprojection or cubemap projection, the stream configuration tool canconvert the input picture to a sinusoidal projection. The sinusoidalprojection can have a single fold or multiple folds (e.g., two-foldprojection). For a single-fold sinusoidal projection, the sinusoidalprojection includes panoramic video content surrounded by empty regions(e.g., with default values such as black or gray). For a two-foldsinusoidal projection, the sinusoidal projection includes panoramicvideo content for two “hemispheres” separated by empty regions (e.g.,with default values such as black or gray). For example, the resolutionof the input pictures in the sinusoidal projection is 8K or higher,which is higher than the input picture in the equirectangularrepresentation. Compared to the equirectangular projection, thesinusoidal projection represents content towards the “poles” of thesphere without excessive stretching, distortion, etc., which can makesubsequent compression operations (such as motion estimation) moreeffective. (In the equirectangular projection, details around the polesare scattered and stretched. Redundancy cannot be exploited as wellduring compression.)

For different values of phi (φ) and theta (θ) in spherical projectioncoordinates, the stream configuration tool splits the input picture(612) into overlapping sections (632), generally as described withreference to FIG. 6a . Since the input picture (612) is in a sinusoidalprojection, however, the overlapping sections (632) can include defaultsample values (e.g., black or gray) for portions in empty regionsoutside of the actual content of the input picture (612). In thepartitioning, the placement of the overlapping sections (632) can beconfigured to reduce the number of default sample values in thesections. Collectively, the overlapping sections (632) still cover allof the actual content of the input picture (612) of panoramic video. InFIG. 6b , the input picture (612) is partitioned into seven overlappingsections. More generally, the number n of sections depends onimplementation (e.g., n is 8, 12, 16, or 32). The extent of overlapbetween the overlapping sections (632) depends on implementation and canbe static or dynamic, generally as described with reference to FIG. 6a .The stream configuration tool can generate various phi/thetacombinations for the overlapping sections (632), generally as describedwith reference to FIG. 6 a.

Although FIG. 6b shows a separate input picture (612) in a sinusoidalprojection, in practice, conversion of an input picture to a sinusoidalprojection can be notional. That is, sample values of the respectiveoverlapping sections (632) in the sinusoidal projection can bedetermined directly from the input picture in an equirectangularprojection, cubemap projection, or other input projection.

The stream configuration tool can create a manifest file, generally asdescribed with reference to FIG. 6a . The stream configuration tool addsthe overlapping sections (632) to corresponding video streams. In FIG.6b , the seven overlapping sections (632) are added to correspondingvideo streams (660 . . . 666), respectively. The stream configurationtool encodes the corresponding video streams (660 . . . 666),respectively, producing bitstreams of encoded data (680 . . . 686) forthe respective sections. Thus, the stream configuration tool encodes themultiple overlapping sections (632) partitioned from the input picture(612) as part of different video streams (660 . . . 666). Section 1 isencoded as a picture of stream 1, section 2 is encoded as a picture ofstream 2, and so on. In this way, different sections of the inputpicture (612) of panoramic video are represented in different bitstreamsof encoded data (680 . . . 686). Finally, the stream configuration toolbuffers the encoded data (680 . . . 686). The encoded data (680 . . .686) can be directly sent to one or more playback tools. In mostconfigurations, however, the encoded data (680 . . . 686) is sent to amedia server, which can also store manifest files with details about theoverlapping sections (632) and streams.

C. Example of Picture of Panoramic Video with Overlapping Sections

FIG. 7 is a diagram illustrating an example (700) of overlappingsections of a picture (710) of panoramic video in a sinusoidalprojection. The picture (710) in the sinusoidal projection has beenpartitioned into seven overlapping sections of equal size. Theoverlapping sections are labeled 0 . . . 6.

FIG. 7 also shows an expanded view of one of the overlappingsection—section 5. Section 5 includes actual content of the picture(710) of panoramic video—shown with no hatching. While section 5includes some actual content that is only part of section 5 (and not anyother section), the overlap regions (740) of section 5 include actualcontent that is also part of one or more other sections (specifically,sections 3, 4, and 6). If a view window moves into one or more of theoverlap regions (740), a playback tool can preemptively fetch contentfor one or more of the adjacent sections that also includes that overlapregion. Section 5 also includes default values (750) (e.g., mid-grayvalues) for empty regions, which are shown with hatching.

D. First Example of Playback Operations for Adaptive Streaming ofPanoramic Video with Overlapping Sections

FIG. 8a shows a first example (801) of playback operations for adaptivestreaming of panoramic video with overlapping sections. In the firstexample (801), overlapping sections (830) of a picture of panoramicvideo are in an equirectangular projection.

A playback tool periodically determines a view window (811) in aspherical projection (810) of the panoramic video for a viewer. Duringplayback, the viewer can control view direction, relative to aviewer/camera position at the center of the panoramic video. The viewermay also be able to control the field of view (e.g., narrow, wide)and/or zoom factor. The view window (811) depends on view direction, andcan also depend on field of view and/or zoom factor.

The playback tool also requests a manifest file from a media server (orstream configuration tool). After receiving the manifest file, theplayback tool identifies which sections of the panoramic video are to beused to create an output picture (890) for the view window (811).Specifically, the playback tool identifies one or more sections thateach contain at least part of the view window (811). FIG. 8a showsoverlapping sections (830) of a picture of panoramic video. In FIG. 8a ,two of the overlapping sections (830)—sections 4 and 5—each contain atleast part of the view window (811), which is shown as a projection(834) onto the picture of panoramic video. The playback tool selects oneor more bitstreams for the identified section(s), respectively.

The playback tool requests encoded data for the selected bitstream(s).For example, depending on configuration, the playback tool requests theencoded data from the stream configuration tool or a media server. Theplayback tool can request encoded data for the selected bitstream(s) ona picture-by-picture basis or some other basis. In the example (801) ofFIG. 8a , the playback tool requests encoded data (854) for bitstream 4and requests encoded data (855) for bitstream 5.

The playback tool receives and decodes the encoded data for the selectedbitstream(s), thereby reconstructing the identified section(s). In theexample (801) of FIG. 8a , the playback tool decodes the encoded data(854) for bitstream 4 to reconstruct section 4 (874), and the playbacktool decodes the encoded data (855) for bitstream 5 to reconstructsection 5 (875).

The playback tool creates an output picture (890) for the view window(811) from the reconstructed section(s). In doing so, for locations ofthe output picture (890), the playback tool selects sample values atcorresponding locations of the reconstructed section(s), or determinessample values at the corresponding locations by interpolating betweenadjacent sample values of the reconstructed section(s). The outputpicture (890) can be in a screen projection (for display) or other(e.g., equirectangular) projection (for subsequent rendering). Thus, tofind the corresponding locations in the reconstructed section(s), theplayback tool can warp between different projections, e.g., from ascreen projection for the output picture to an equirectangularprojection for the overlapping sections (830). The playback tool canalso perform various post-processing operations (e.g., color conversionto a color space appropriate for a display device).

During playback, if the view window (811) changes, the playback tool canidentify new sections/bitstreams to be used to create an output picture(890) for the view window (811). Because of the overlap between adjacentsections, for changes in view direction and/or zoom factor that aregradual and consistent, the playback tool can, in effect, preemptivelyfetch a new section as the view window (811) moves out of a currentsection into the new section. By the time the view window (811) reachesa non-overlapping part of the new section, content for the new sectionhas already been retrieved and reconstructed. In this way, the playbacktool can hide network latency and stream switching latency from theviewer, and disruption of playback is avoided.

E. Second Example of Playback Operations for Adaptive Streaming ofPanoramic Video with Overlapping Sections

FIG. 8b shows a second example (802) of playback operations for adaptivestreaming of panoramic video with overlapping sections. In the secondexample (802), overlapping sections (831) of a picture of panoramicvideo are in a sinusoidal projection. The overlapping sections (831) ofthe picture of panoramic video can be organized as described withreference to the example (602) of FIG. 6 b.

As in the example (801) of FIG. 8a , a playback tool periodicallydetermines a view window (811) in a spherical projection (810) of thepanoramic video for a viewer. After receiving a manifest file, theplayback tool identifies which of the overlapping sections (831) of thepanoramic video are to be used to create an output picture (892) for theview window (811). Specifically, the playback tool identifies one ormore of the overlapping sections (831) that each contain at least partof the view window (811). In FIG. 8b , two of the overlapping sections(831)—sections 2 and 6—each contain at least part of the view window(811), which is shown as a projection (832) onto the picture ofpanoramic video. The playback tool selects one or more bitstreams forthe identified section(s), respectively.

The playback tool requests encoded data for the selected bitstream(s),generally as described with reference to FIG. 8a . In the example (802)of FIG. 8b , the playback tool requests encoded data (852) for bitstream2 and requests encoded data (856) for bitstream 6. The playback toolreceives and decodes the encoded data for the selected bitstream(s),thereby reconstructing the identified section(s). In the example (802)of FIG. 8b , the playback tool decodes the encoded data (852) forbitstream 2 to reconstruct section 2 (872), and the playback tooldecodes the encoded data (856) for bitstream 6 to reconstruct section 6(876). The playback tool creates an output picture (892) for the viewwindow (811) from the reconstructed section(s), generally as describedwith reference to FIG. 8a . To find the corresponding locations in thereconstructed section(s), the playback tool can warp between differentprojections, e.g., from a screen projection for the output picture to asinusoidal projection for the overlapping sections (831).

VII. Example Techniques for Stream Configuration of Panoramic Video withOverlapping Sections

FIG. 9 shows an example technique (900) for stream configuration ofpanoramic video with overlapping sections. A panoramic video streamconfiguration tool as described with reference to FIG. 4, or otherpanoramic video stream configuration tool, can perform the exampletechnique (900).

The stream configuration tool receives (910) an input picture ofpanoramic video. Typically, the input picture is in an input projectionsuch as an equirectangular projection, a cubemap projection, or asinusoidal projection. The stream configuration tool splits (920) theinput picture into multiple overlapping sections according to partitionsettings. For example, the partition settings include the count ofsections, sizes of sections, positions of sections, and extent ofoverlap between sections. Each of the multiple sections overlaps atleast one other section among the multiple sections. (This ultimatelydecreases overall compression efficiency but facilitates reduction ofincidence of disruption attributable to bitstream switching duringplayback of the panoramic video.) For example, for each of the multiplesections, the section overlaps each adjacent section among the multiplesections.

In some configurations, the stream configuration tool projects the inputpicture from an input projection to an intermediate projection whensplitting the input picture into multiple sections (in the intermediateprojection). For example, the input projection is an equirectangularprojection or a cubemap projection, and the intermediate projection is asinusoidal projection. When the multiple sections are in a sinusoidalprojection, at least one of the multiple sections may include at leastsome sample values having default values (e.g., black values or grayvalues, not representing content of the input picture of panoramicvideo).

The stream configuration tool adds (930) the multiple sections,respectively, to corresponding video streams for encoding.

FIG. 9 shows two loops. As part of a loop for a formatting pipeline, thestream configuration tool checks (940) whether to continue operationsfor a next input picture. If so, the stream configuration tool receives(910) the next input picture, splits (920) it into multiple overlappingsections, and adds (930) the sections to corresponding video streams. Inthis way, the stream configuration tool iteratively splits inputpictures and adds sections for the input pictures to corresponding videostreams.

As part of an encoding pipeline, the stream configuration tool encodes(950) the multiple sections in the corresponding video streams,respectively, for an input picture. This produces encoded data for themultiple sections as part of multiple bitstreams for the correspondingvideo streams, respectively. Typically, the bitstreams are videoelementary bitstreams. The encoded data in the video elementarybitstreams can be multiplexed into a single container stream fordelivery to a media server. The stream configuration tool stores (960)the encoded data for delivery (e.g., to a media server, or directly toone or more panoramic video playback tools). The stream configurationtool checks (970) whether to continue encoding operations and, if so,encodes (950) the sections of the next input picture. In this way, aspart of a loop for the encoding pipeline, the stream configuration toolencodes the sections of pictures added to video streams in theformatting pipeline.

The stream configuration tool can also produce one or more manifestfiles. The manifest file(s) include information indicating, for each ofthe multiple bitstreams, the position of one of the multiple sections(in terms of an input projection or spherical projection) whose contentis part of the corresponding video stream for that bitstream. Forexample, for each section, the manifest file includes phi and thetacoordinates for the section. The stream configuration tool can deliverthe manifest file(s) to a media server, for subsequent delivery to oneor more playback tools. Or, the stream configuration tool can directlydeliver the manifest file(s) to one or more playback tools. The manifestfile(s) can be delivered as user data of elementary bitstreams, asmetadata in a container, or in some other way. Alternatively, the streamconfiguration tool and playback tool(s) can operate without exchanginginformation in manifest file(s), and input pictures are partitioned intosections according to a static, pre-defined pattern.

In some configurations, the partition settings can adaptively change.For example, the stream configuration tool can receive an indication offeedback and, based at least in part on the indication of feedback,adjust the partition settings. The indication of feedback can include anindication of network connection quality, an indication of magnitude ofview window change activity, an indication of which view direction isprevalent, and/or some other type of feedback. To adjust the partitionsettings, the stream configuration tool can change an extent of overlapbetween the multiple sections. For example, if network connectionquality is poor or view window change activity is high, the streamconfiguration tool can increase the extent of overlap between adjacentsections. Or, if network connection quality is good and view windowchange activity is low, the stream configuration tool can decrease theextent of overlap between adjacent sections. Alternatively, the streamconfiguration tool can change the count of overlapping sections, changerelative sizes of at least some of the overlapping sections, changepositions of at least some of the overlapping sections, add one or moresections, at new positions, to the overlapping sections, and/or removeone or more sections from the overlapping sections. For example, inresponse to an indication of which view direction is prevalent, thestream configuration tool can add one or more sections or re-positionsections to focus on the prevalent view direction (and thereby reducethe incidence of switching around the prevalent view direction).Alternatively, the stream configuration tool can make some other changeto the partition settings.

VIII. Example Techniques for Playback of Panoramic Video withOverlapping Sections

FIG. 10 shows an example technique (1000) for playback of panoramicvideo with overlapping sections. A panoramic video playback tool asdescribed with reference to FIG. 5, or other panoramic video playbacktool, can perform the example technique (1000).

The panoramic video playback tool determines (1010) a view window forplayback of panoramic video. For example, the view window depends onview direction, field of view, and/or zoom factor. The playback tool canreceive an indication of a view direction for an application. Forexample, the indication of the view direction is a set of heading,pitch, and roll values for the view direction. Or, the indication of theview direction is a set of affine transform coefficients that specify aspatial rotation for the view direction. Or, the view direction isspecified in some other way. The playback tool can receive theindication of the view direction from the application or from a sourcespecified by the application. The playback tool can also receive anindication of a field of view and/or zoom factor for the application.

From among multiple sections of the panoramic video, the playback toolidentifies (1020) one or more sections that contain at least part of theview window. Each of the multiple sections overlaps at least one othersection among the multiple sections, which reduces incidence ofdisruption attributable to bitstream switching. For example, theplayback tool identifies each of the overlapping sections that containsat least part of the view window. For the identified section(s), theplayback tool selects (1030) one or more bitstreams among multiplebitstreams for corresponding video streams.

FIG. 10 shows two loops. As part of a loop for a view window pipeline,the playback tool checks (1040) whether there has been a change to theview window (e.g., due to a change in view direction, field of view, orzoom factor). If so, the playback tool determines (1010) the viewwindow, identifies (1020) the section(s) that contain the view window,and selects (1030) the bitstream(s) for the identified section(s). Inthis way, the playback tool can iteratively perform operations todetermine (1010) the view window, identify (1020) the section(s) thatcontain at least part of the view window, and select (1030) thebitstream(s) for the identified section(s).

As part a decoding and reconstruction pipeline, the playback toolrequests (1050) encoded data, in the selected bitstream(s) for theidentified section(s), respectively, for an input picture of thepanoramic video. Depending on configuration, the playback tool canrequest the encoded data from a media server or directly from apanoramic video stream configuration tool. The playback tool can makeseparate requests for portions of an input picture or for each inputpicture, or the playback tool can batch requests.

The playback tool receives (1060) the encoded data (e.g., from a mediaserver, or directly from a panoramic video stream configuration tool).The playback tool decodes (1070) the encoded data to reconstruct samplevalues for the identified section(s) for the input picture. Then, basedat least in part on the reconstructed section(s), the playback toolcreates (1080) an output picture. When creating the output picture, theplayback tool can project the reconstructed section(s) from an inputprojection (e.g., an equirectangular projection) or an intermediateprojection (e.g., sinusoidal projection) to an output projection (e.g.,screen projection). The playback tool stores (1090) the output picturefor output to a display device. The playback tool checks (1095) whetherto continue decoding and reconstruction operations and, if so, requests(1050) and decodes (1070) encoded data for one or more sections of thenext input picture. In this way, as part of a loop for the decoding andreconstruction pipeline, the playback tool reconstructs sectionsidentified in the view window pipeline.

The playback tool can receive one or more manifest files (e.g., from amedia server or directly from a stream configuration tool). The manifestfile(s) include information indicating, for each of the multiplebitstreams, the position of one of the multiple sections (in terms of aninput projection or spherical projection) whose content is part of thecorresponding video stream for that bitstream. For example, for eachsection, the manifest file includes phi and theta coordinates for thesection. The playback tool can use the manifest file(s) to identify(1020) the section(s) that contain at least part of the view windowand/or select (1030) the bitstream(s) for the identified sections. Theplayback tool can also use the manifest file(s) when creating (1080) theoutput picture based on the reconstructed section(s). The manifestfile(s) can be delivered as user data of elementary bitstreams, asmetadata in a container, or in some other way. Alternatively, the streamconfiguration tool and playback tool(s) can operate without exchanginginformation in manifest file(s), and input pictures are partitioned intosections according to a static, pre-defined pattern.

The playback tool can send an indication of feedback to a streamconfiguration tool or intermediary that aggregates feedback. Theindication of feedback can include an indication of network connectionquality, an indication of magnitude of view window change activity, anindication of which view direction is prevalent, and/or some other typeof feedback. The feedback can be used to adjust partition settings, forexample, as described in the previous section.

IX. Examples of Panoramic Video Streaming with Composite Pictures

This section describes examples of panoramic video streaming withcomposite pictures. Some examples relate to stream configurationoperations, and other examples relate to playback operations.

A composite picture includes a high-resolution section of an inputpicture of panoramic video as well as a low-resolution version of theinput picture. Under normal operation, a playback tool can usereconstructed high-resolution section(s) to render high-quality views ofthe panoramic video. If the view window drastically changes, however, orif encoded data for a specific section is lost or corrupted, theplayback tool can temporarily use the low-resolution version of theinput picture to render lower-quality details for views of the panoramicvideo, without disruption of playback, until encoded data for thehigh-resolution section(s) is retrieved or recovered.

Using composite pictures of panoramic video can decrease overallcompression efficiency, because sample values for low-resolutionversions of input pictures, which might not be used in rendering at all,are redundantly encoded. That is, extra bits are used for encoded datafor the low-resolution versions of the input pictures. On the otherhand, using composite pictures also tends to reduce the incidence ofplayback disruption when a view window drastically changes or encodeddata for a high-resolution section is lost or corrupted. When a viewwindow changes drastically, switching to a new bitstream for a newsection can take time (e.g., to send the request for the new bitstreamto a media server, and to wait for a switch point at which decoding canbegin in the new bitstream). Similarly, when encoded data for ahigh-resolution section is lost or corrupted, recovering encoded data ofthe bitstream for the section can take time. Until encoded data for thehigh-resolution section(s) is retrieved/recovered, the playback tool canuse the low-resolution version of the input picture to renderlower-quality details for views of the panoramic video, withoutdisruption of playback. This hides network latency and stream switchinglatency from the viewer, and disruption of playback is avoided.

A. First Example of Stream Configuration Operations for AdaptiveStreaming of Panoramic Video with Composite Pictures

FIG. 11a shows a first example (1101) of stream configuration operationsfor adaptive streaming of panoramic video with composite pictures. Inthe first example (1101), an input picture (1110) of panoramic video isin an equirectangular projection.

With reference to FIG. 11a , a stream configuration tool receives orcreates a series of input pictures—such as the input picture (1110)—inan equirectangular projection. The input pictures can be created frommultiple camera video streams (associated with different views from acentral position) or from a video stream from an omnidirectional camera.For example, the resolution of the input pictures in the equirectangularprojection is 4K (3840×2160) or higher.

For different values of phi (φ) and theta (θ) in spherical projectioncoordinates, the stream configuration tool splits the input picture(1110) into sections (1120). The sections (1120) can be non-overlappingor, as described section VI, overlapping. In general, the sections(1120) are associated with different view directions. Each of thesections (1120) corresponds to a region of the surface of the sphere forthe panoramic video, and is parameterized using a range of phi and thetacoordinates for the surface of the sphere. Alternatively, the sections(1120) can be parameterized in some other way. The sections (1120) canhave the same size or different sizes. For example, each of the sections(1120) has a spatial resolution of 1080p, 720p, or some other size.Collectively, the sections (1120) cover all of the actual content of theinput picture (1110). In FIG. 11a , the input picture (1110) ispartitioned into six non-overlapping sections. More generally, thenumber n of sections depends on implementation (e.g., n is 8, 12, 16, or32).

By default, the input picture (1110) is always partitioned in the sameway (or in a way that depends on resolution of the input picture (1110),picture size for the video streams to be encoded, or other factors knownat the start of stream configuration). Alternatively, the count ofsections (1120) and sizes of sections (1120) can be configurable and/oradjustable during stream configuration and playback.

The stream configuration tool can generate as many phi/thetacombinations as desired for the overlapping sections (1120). Thesecombinations can be preset or adapted to a requested view. For example,the “center” of the partitioning pattern can change, based on where thefocus (or expected focus) of most view windows will be. If there is asection/stream centered at the focus, a playback tool might not need torequest and combine sections from multiple bitstreams. Alternatively, anew section could simply be added, centered at the focus.

The stream configuration tool also creates a manifest file (not shown)that indicates the spherical coordinates associated with the respectivesections (1120). Alternatively, parameters can be sent in some other wayfor each of the sections (1120), indicating what part of the inputpicture (1110) is covered by that section. The parameters can be valuesof phi and theta per section or other information used to derive thesame information about the scope of the section.

The stream configuration tool creates a low-resolution version (1130) ofthe input picture of panoramic video. For example, the streamconfiguration tool downsamples the input picture (1110) of panoramicvideo. The stream configuration tool can downsample the input picture(1110) by the same factor horizontally and vertically, or by differentfactors horizontally and vertically.

The stream configuration tool adds the sections (1120) and thelow-resolution version of the input picture to composite pictures (1140. . . 1145). For each one of the sections (1120), the streamconfiguration tool combines that section and the low-resolution version(1130) of the input picture to make a corresponding one of the compositepictures (1140 . . . 1145). In this way, the stream configuration toolcreates a different composite picture for each of the sections (1120).For example, composite picture 0 (1140) includes section 0 and thelow-resolution version (1130) of the input picture. Composite picture 5(1140) includes section 5 and the low-resolution version (1130) of theinput picture.

In the example (1101) of FIG. 11a , the low-resolution version (1130) ofthe input picture is in an equirectangular projection. Alternatively,the low-resolution version (1130) of the input picture can be in asinusoidal projection or other projection. The low-resolution version(1130) of the input picture can be in the same projection as thesections (1120) (e.g., both sinusoidal or both equirectangular) ordifferent projection (e.g., sinusoidal for the sections (1120),equirectangular for the low-resolution version (1130) of the inputpicture).

The low-resolution version (1130) of the input picture can be put in thecomposite pictures (1140 . . . 1145) at a predefined location. Or, thelocation can be specified, e.g., in a manifest file. The low-resolutionversion (1130) of the input picture can be composited below one thesections (1120) or arranged in some other configuration in a singlepicture. Alternatively, the composite picture can be organized asmultiple views in a frame packing arrangement.

The stream configuration tool adds the composite pictures (1140 . . .1145) to corresponding video streams. In FIG. 11a , the six compositepictures (1140 . . . 1145) are added to corresponding video streams(1150 . . . 1155), respectively.

The stream configuration tool encodes the corresponding video streams(1150 . . . 1155), respectively, producing bitstreams of encoded data(1170 . . . 1175) for the respective composite pictures. Thus, thestream configuration tool encodes the composite pictures (1140 . . .1145), including different sections (1120) of the input picture (1110),as part of different video streams (1150 . . . 1155). Composite picture1 is encoded as a picture of stream 1, composite picture 2 is encoded asa picture of stream 2, and so on. In this way, composite pictures fordifferent sections of the input picture (1110) of panoramic video arerepresented in different bitstreams of encoded data (1170 . . . 1175).

Finally, the stream configuration tool buffers the encoded data (1170 .. . 1175). The encoded data (1170 . . . 1175) can be directly sent toone or more playback tools. In most configurations, however, the encodeddata (1170 . . . 1175) is sent to a media server. The media server canalso store a manifest file with details about the sections (1120) andstreams.

B. Second Example of Stream Configuration Operations for AdaptiveStreaming of Panoramic Video with Composite Pictures

FIG. 11b shows a second example (1102) of stream configurationoperations for adaptive streaming of panoramic video with compositepictures. In the second example (1102), the input picture (1112) is in asinusoidal projection, and the input picture (1112) is split intooverlapping sections (1122).

With reference to FIG. 11b , the stream configuration tool receives orcreates a series of input pictures—such as the input picture (1112)—in asinusoidal projection. From an input picture in an equirectangularprojection or cubemap projection, the stream configuration tool canconvert the input picture to a sinusoidal projection, as described withreference to the example (602) of FIG. 6 b.

For different values of phi (φ) and theta (θ) in spherical projectioncoordinates, the stream configuration tool splits the input picture(1112) into overlapping sections (1122), generally as described insection VI. Since the input picture (1112) is in a sinusoidalprojection, the overlapping sections (1122) can include default samplevalues (e.g., black or gray) for portions in empty regions outside ofthe actual content of the input picture (1112). In FIG. 11b , the inputpicture (1112) is partitioned into seven overlapping sections. Moregenerally, the number n of sections depends on implementation (e.g., nis 8, 12, 16, or 32). The extent of overlap between the overlappingsections (1122) depends on implementation and can be static or dynamic,as described in section VI. The stream configuration tool can create amanifest file that includes information about the sections (1122), asdescribed in section VI.

Although FIG. 11b shows a separate input picture (1112) in a sinusoidalprojection, in practice, conversion of an input picture to a sinusoidalprojection can be notional. That is, sample values of the respectiveoverlapping sections (1122) in the sinusoidal projection can bedetermined directly from the input picture in an equirectangularprojection, cubemap projection, or other input projection.

As described with reference to the example (1101) of FIG. 11a , thestream configuration tool creates a low-resolution version (1132) of theinput picture of panoramic video. The low-resolution version (1132) ofthe input picture can be in the same projection as the sections (1122)(e.g., both sinusoidal) or different projection (e.g., sinusoidal forthe sections (1122), equirectangular for the low-resolution version(1132) of the input picture).

The stream configuration tool adds the sections (1122) and thelow-resolution version (1132) of the input picture to composite pictures(1190 . . . 1196). For each one of the sections (1122), the streamconfiguration tool combines that section and the low-resolution version(1132) of the input picture to make a corresponding one of the compositepictures (1190 . . . 1196). In this way, the stream configuration toolcreates a different composite picture for each of the sections (1122).For example, composite picture 0 (1190) includes section 0 and thelow-resolution version (1132) of the input picture. Composite picture 6(1196) includes section 6 and the low-resolution version (1132) of theinput picture.

The low-resolution version (1132) of the input picture can be put in thecomposite pictures (1190 . . . 1196) at a predefined location. Or, thelocation can be specified, e.g., in a manifest file. The low-resolutionversion (1132) of the input picture can be composited below one thesections (1122) or arranged in some other configuration in a singlepicture. Alternatively, a composite picture can be organized as multipleviews in a frame packing arrangement.

The stream configuration tool adds the composite pictures (1190 . . .1196) to corresponding video streams. In FIG. 11b , the seven compositepictures (1190 . . . 1196) are added to corresponding video streams(1160 . . . 1166), respectively. The stream configuration tool encodesthe corresponding video streams (1160 . . . 1166), respectively,producing bitstreams of encoded data (1180 . . . 1186) for therespective composite pictures. Thus, the stream configuration toolencodes the composite pictures (1190 . . . 1196), including differentsections (1122) of the input picture (1112), as part of different videostreams (1160 . . . 1166).

Finally, the stream configuration tool buffers the encoded data (1180 .. . 1186). The encoded data (1180 . . . 1186) can be directly sent toone or more playback tools. In most configurations, however, the encodeddata (1180 . . . 1186) is sent to a media server. The media server canalso store a manifest file with details about the sections (1122) andstreams.

C. Example of Composite Picture

FIG. 12 is a diagram illustrating an example composite picture (1200) ofpanoramic video. The composite picture (1200) includes a section (1220)of an input picture. For example, the section (1220) is ahigh-resolution section partitioned from an input picture in anequirectangular projection, cubemap projection, sinusoidal projection,or other projection. The composite picture (1200) also includes alow-resolution version (1230) of the input picture. The low-resolutionversion (1230) of the input picture depicts the entire input picture,albeit at a lower spatial resolution than the original input picture.The low-resolution version (1230) of the input picture can be in anequirectangular projection, cubemap projection, sinusoidal projection,or other projection. In FIG. 12, the low-resolution version (1230) ofthe input picture is below the section (1220) of the input picture.Alternatively, the composite picture (1200) can be organized in someother way.

D. First Example of Playback Operations for Adaptive Streaming ofPanoramic Video with Composite Pictures

FIG. 13a shows a first example (1301) of playback operations foradaptive streaming of panoramic video with composite pictures. In thefirst example (1301), sections (1330) of a picture of panoramic videoare in an equirectangular projection.

A playback tool periodically determines a view window (1311) in aspherical projection (1310) of the panoramic video for a viewer. Duringplayback, the viewer can control view direction, relative to aviewer/camera position at the center of the panoramic video. The viewermay also be able to control the field of view (e.g., narrow, wide)and/or zoom factor. The view window (1311) depends on view direction,and can also depend on field of view and/or zoom factor.

The playback tool also requests a manifest file from a media server (orstream configuration tool). After receiving the manifest file, theplayback tool identifies which sections of the panoramic video are to beused to create an output picture (1390) for the view window (1311).Specifically, the playback tool identifies one or more sections thateach contain at least part of the view window (1311). FIG. 13a showsnon-overlapping sections (1330) of a picture of panoramic video. In FIG.13a , one of the sections (1330)—section 4—contains the view window(1311), which is shown as a projection (1334) onto the picture ofpanoramic video. The playback tool selects one or more bitstreams forthe identified section(s), respectively.

The playback tool requests encoded data for the selected bitstream(s).For example, depending on configuration, the playback tool requests theencoded data from the stream configuration tool or a media server. Theplayback tool can request encoded data for the selected bitstream(s) ona picture-by-picture basis or some other basis. In the example (1301) ofFIG. 13a , the playback tool requests encoded data (1354) for bitstream4.

The playback tool receives and decodes the encoded data for the selectedbitstream(s), thereby reconstructing composite picture(s) that includethe identified section(s). In the example (1301) of FIG. 13a , theplayback tool decodes the encoded data (1354) for bitstream 4 toreconstruct a composite picture (1364) that includes section 4.

The playback tool creates an output picture (1390) for the view window(1311) from the reconstructed section(s) and/or the reconstructedlow-resolution version of the input picture. For a normal mode of outputpicture creation, the reconstructed high-resolution section(s) of thecomposite picture(s) support rendering of high-resolution views/detailsfrom the content of the section(s). In FIG. 13a , the reconstructedsection(s) include section 4. For locations of the output picture(1390), the playback tool selects sample values at correspondinglocations of the reconstructed section(s), or determines sample valuesat the corresponding locations by interpolating between adjacent samplevalues of the reconstructed section(s). So long as the view window(1311) falls within the reconstructed section(s), the playback tool canrender a high-quality view.

If the view window (1311) falls outside the reconstructed section(s),however, the playback tool uses a fallback mode of output picturecreation. In the fallback mode, the playback tool can render low-qualityviews/details from the low-resolution version of the compositepicture(s), without requesting additional content from the streamconfiguration tool or media server. For locations of the output picture(1390), the playback tool selects sample values at correspondinglocations of the reconstructed low-resolution version of the inputpicture, or determines sample values at the corresponding locations byinterpolating between adjacent sample values of the reconstructedlow-resolution version of the input picture. The playback tool can scaleup, etc. the low-resolution version of the input picture beforerendering. Thus, the low-resolution version of the input picturesupports rendering of lower-resolution views/details, as needed, if theview direction or zoom factor dramatically changes or encoded data for ahigh-resolution section is lost. In this way, rendering operations arenot interrupted during playback, although quality of rendered views maytemporarily suffer.

The output picture (1390) can be in a screen projection (for display) orother (e.g., equirectangular) projection (for subsequent rendering). Tofind the corresponding locations in the reconstructed section(s) and/orreconstructed low-resolution version of the input picture, the playbacktool can warp between different projections, e.g., from a screenprojection for the output picture to an equirectangular projection forthe sections (1330). The playback tool can also perform variouspost-processing operations (e.g., color conversion to a color spaceappropriate for a display device).

During playback, if the view window (1311) changes, the playback toolcan identify new sections/bitstreams to be used to create an outputpicture (1390) for the view window (1311). If there is a sudden,dramatic change in view direction and/or zoom factor, or if encoded datafor a high-resolution section is lost, however, the playback tool canrender views/details from the low-resolution version of the inputpicture until encoded data for high-resolution section(s) is retrievedor recovered. In this way, the playback tool can hide network latencyand stream switching latency from the viewer, and disruption of playbackis avoided.

E. Second Example of Playback Operations for Adaptive Streaming ofPanoramic Video with Composite Pictures

FIG. 13b shows a second example (1302) of playback operations foradaptive streaming of panoramic video with composite pictures. In thesecond example (1302), overlapping sections (1331) of a picture ofpanoramic video are in a sinusoidal projection. The overlapping sections(1331) of the picture of panoramic video can be organized as describedwith reference to the example (602) of FIG. 6b and example (1102) ofFIG. 11 b.

As in the example (1301) of FIG. 13a , a playback tool periodicallydetermines a view window (1311) in a spherical projection (1310) of thepanoramic video for a viewer. After receiving a manifest file, theplayback tool identifies which of the overlapping sections (1331) of thepanoramic video are to be used to create an output picture (1392) forthe view window (1311). Specifically, the playback tool identifies oneor more of the overlapping sections (1331) that each contain at leastpart of the view window (1311). In FIG. 13b , two of the overlappingsections (1331)—sections 2 and 6—each contain at least part of the viewwindow (1311), which is shown as a projection (1332) onto the picture ofpanoramic video. The playback tool selects one or more bitstreams forthe identified section(s), respectively.

The playback tool requests encoded data for the selected bitstream(s),generally as described with reference to FIG. 13a . In the example(1302) of FIG. 13b , the playback tool requests encoded data (1352) forbitstream 2 and requests encoded data (1356) for bitstream 6. Theplayback tool receives and decodes the encoded data for the selectedbitstream(s), thereby reconstructing composite picture(s) that includethe identified section(s). In the example (1302) of FIG. 13b , theplayback tool decodes the encoded data (1352) for bitstream 2 toreconstruct a composite picture (1362) that includes section 2, and theplayback tool decodes the encoded data (1356) for bitstream 6 toreconstruct a composite picture (1366) that includes section 6.

The playback tool creates an output picture (1392) for the view window(1311) from the reconstructed section(s) and/or the reconstructedlow-resolution version of the input picture, generally as described withreference to FIG. 13a . For a normal mode of output picture creation,the reconstructed high-resolution section(s) of the composite picture(s)support rendering of high-resolution views/details from the content ofthe section(s). In FIG. 13b , the reconstructed section(s) includesection 2 and section 6. So long as the view window (1311) falls withinthe reconstructed section(s), the playback tool can render ahigh-quality view. If the view window (1311) falls outside thereconstructed section(s) (in FIG. 6, sections 2 and 6), the playbacktool uses a fallback mode of output picture creation. In the fallbackmode, the playback tool can render low-quality views/details from thelow-resolution version of the composite picture(s), without requestingadditional content from the stream configuration tool or media server.Thus, the low-resolution version of the input picture supports renderingof lower-resolution views/details, as needed, if the view direction orzoom factor dramatically changes or encoded data for a high-resolutionsection is lost. To find the corresponding locations in thereconstructed section(s) and/or reconstructed low-resolution version ofthe input picture, the playback tool can warp between differentprojections, e.g., from a screen projection for the output picture to asinusoidal projection for the overlapping sections (1331).

X. Example Techniques for Stream Configuration of Panoramic Video withComposite Pictures

FIG. 14 shows an example technique (1400) for stream configuration ofpanoramic video with composite pictures. A panoramic video streamconfiguration tool as described with reference to FIG. 4, or otherpanoramic video stream configuration tool, can perform the exampletechnique (1400).

The stream configuration tool receives (1410) an input picture ofpanoramic video. Typically, the input picture is in an input projectionsuch as an equirectangular projection, a cubemap projection, or asinusoidal projection. The input picture has a spatial resolution suchas 4K or higher.

The stream configuration tool creates (1420) a low-resolution version ofthe input picture. For example, the stream configuration tooldownsamples the input picture horizontally and/or vertically. Thelow-resolution version of the input picture can be in an inputprojection (e.g., an equirectangular projection, a cubemap projection,or a sinusoidal projection) or intermediate projection (e.g., asinusoidal projection). In general, the low-resolution version of theinput picture has a lower spatial resolution than the input picture.

The stream configuration tool also splits (1430) the input picture intomultiple sections according to partition settings. The sections can beoverlapping sections, as described above, or non-overlapping sections.For example, the partition settings include the count of sections, sizesof sections, positions of sections, and extent of overlap betweensections. In some configurations, the stream configuration tool projectsthe input picture from an input projection to an intermediate projectionwhen splitting the input picture into multiple sections (in theintermediate projection). For example, the input projection (for theinput picture and low-resolution version of the input picture) is anequirectangular projection or a cubemap projection, and the intermediateprojection is a sinusoidal projection. When the multiple sections are ina sinusoidal projection, at least one of the multiple sections mayinclude at least some sample values having default values (e.g., blackvalues or gray values, not representing content of the input picture ofpanoramic video). In general, each of the sections has a spatialresolution that is lower than the spatial resolution of the inputpicture, but may be higher or lower than the spatial resolution of thelow-resolution version of the input picture.

The stream configuration tool creates (1440) multiple compositepictures. Each of the composite pictures includes one of the multiplesections and also includes the low-resolution version of the inputpicture. For example, within each of the composite pictures, thelow-resolution version of the input picture is adjacent one of thesections. Within each of the composite pictures, the low-resolutionversion of the input picture can be positioned at a pre-defined locationrelative to the one of the multiple sections. Alternatively, for each ofthe composite pictures, one of the multiple sections provides a firstview of a frame packing arrangement, and the low-resolution version ofthe input picture provides a second view of the frame packingarrangement. Alternatively, the composite pictures are organized in someother way. The stream configuration tool adds (1450) the multiplecomposite pictures, respectively, to corresponding video streams forencoding.

FIG. 14 shows two loops. As part of a loop for a formatting pipeline,the stream configuration tool checks (1460) whether to continueoperations for a next input picture. If so, the stream configurationtool receives (1410) the next input picture, creates (1420) alow-resolution version of the next input picture, splits (1430) the nextinput picture into multiple sections, creates (1440) composite picturesfor the next input picture, and adds (1450) the composite pictures tocorresponding video streams. In this way, the stream configuration tooliteratively creates composite pictures and adds them to correspondingvideo streams.

As part of an encoding pipeline, the stream configuration tool encodes(1470) the multiple composite pictures in the corresponding videostreams, respectively, for an input picture. This produces encoded datafor the composite pictures as part of multiple bitstreams for thecorresponding video streams, respectively. Typically, the bitstreams arevideo elementary bitstreams. The encoded data in the video elementarybitstreams can be multiplexed into a single container stream fordelivery to a media server. The stream configuration tool stores (1480)the encoded data for delivery (e.g., to a media server, or directly toone or more panoramic video playback tools). The stream configurationtool checks (1490) whether to continue encoding operations and, if so,encodes (1470) the composite pictures for the next input picture. Inthis way, as part of a loop for the encoding pipeline, the streamconfiguration tool encodes the composite pictures added to video streamsin the formatting pipeline.

The stream configuration tool can also produce one or more manifestfiles. The manifest file(s) include information indicating, for each ofthe multiple bitstreams, the position of one of the multiple sections(in terms of an input projection or spherical projection) whose contentis part of the corresponding video stream for that bitstream. Forexample, for each section, the manifest file includes phi and thetacoordinates for the section. The manifest file(s) can also includeinformation that indicates where the low-resolution version of the inputpicture is positioned in the composite pictures, respectively. Thestream configuration tool can deliver the manifest file(s) to a mediaserver, for subsequent delivery to one or more playback tools. Or, thestream configuration tool can directly deliver the manifest file(s) toone or more playback tools. The manifest file(s) can be delivered asuser data of elementary bitstreams, as metadata in a container, or insome other way. Alternatively, the stream configuration tool andplayback tool(s) can operate without exchanging information in manifestfile(s), and input pictures are partitioned into sections according to astatic, pre-defined pattern.

XI. Example Techniques for Playback of Panoramic Video with CompositePictures

FIG. 15 shows an example technique (1500) for playback of panoramicvideo with composite pictures. A panoramic video playback tool asdescribed with reference to FIG. 5, or other panoramic video playbacktool, can perform the example technique (1500).

The panoramic video playback tool determines (1510) a view window forplayback of panoramic video. For example, the view window depends onview direction, field of view, and/or zoom factor. The playback tool canreceive an indication of a view direction for an application. Forexample, the indication of the view direction is a set of heading,pitch, and roll values for the view direction. Or, the indication of theview direction is a set of affine transform coefficients that specify aspatial rotation for the view direction. Or, the view direction isspecified in some other way. The playback tool can receive theindication of the view direction from the application or from a sourcespecified by the application. The playback tool can also receive anindication of a field of view and/or zoom factor for the application.

From among multiple sections of the panoramic video, the playback toolidentifies (1520) one or more sections that contain at least part of theview window. The sections can be overlapping sections, which reducesincidence of disruption attributable to bitstream switching, ornon-overlapping sections. For example, the playback tool identifies eachof the multiple sections that contains at least part of the view window.For the identified section(s), the playback tool selects (1530) one ormore bitstreams among multiple bitstreams for corresponding videostreams.

FIG. 15 shows two loops. As part of a loop for a view window pipeline,the playback tool checks (1540) whether there has been a change to theview window (e.g., due to a change in view direction, field of view, orzoom factor). If so, the playback tool determines (1510) the viewwindow, identifies (1520) the section(s) that contain the view window,and selects (1530) the bitstream(s) for the identified section(s). Inthis way, the playback tool can iteratively perform operations todetermine (1510) the view window, identify (1520) the section(s) thatcontain at least part of the view window, and select (1530) thebitstream(s) for the identified section(s).

As part a decoding and reconstruction pipeline, the playback toolrequests (1550) encoded data, in the selected bitstream(s) for theidentified section(s), respectively, for an input picture of thepanoramic video. Depending on configuration, the playback tool canrequest the encoded data from a media server or directly from apanoramic video stream configuration tool. The playback tool can makeseparate requests for portions of an input picture or for each inputpicture, or the playback tool can batch requests.

Each of the identified section(s) is part of a composite picture thatalso includes a low-resolution version of an input picture. Eachcomposite picture includes one of the multiple sections and alsoincludes the low-resolution version of the input picture. For example,for each composite picture, the low-resolution version of the inputpicture is adjacent one of the multiple sections within the compositepicture. For each composite picture, the low-resolution version of theinput picture and the one of the multiple sections can be located atpre-defined positions within the composite picture. Alternatively, foreach composite picture, one of the multiple sections provides a firstview of a frame packing arrangement, and the low-resolution version ofthe input picture provides a second view of the frame packingarrangement. Alternatively, the composite pictures are organized in someother way.

Typically, the input picture is in an input projection such as anequirectangular projection, a cubemap projection, or a sinusoidalprojection. The input picture has a spatial resolution such as 4K orhigher. The low-resolution version of the input picture can be in aninput projection (e.g., an equirectangular projection, a cubemapprojection, or a sinusoidal projection) or intermediate projection(e.g., a sinusoidal projection). In general, the low-resolution versionof the input picture has a lower spatial resolution than the inputpicture. In general, each of the multiple sections has a spatialresolution that is lower than the spatial resolution of the inputpicture, but may be higher or lower than the spatial resolution of thelow-resolution version of the input picture.

The playback tool receives (1560) the encoded data (e.g., from a mediaserver, or directly from a panoramic video stream configuration tool).The playback tool decodes (1570) the encoded data to reconstruct samplevalues for the identified section(s) for the input picture and/orreconstruct sample values for the low-resolution version of the inputpicture. For example, the playback tool reconstructs both the identifiedsection(s) and the low-resolution version of the input picture. Or, ifthe view window is entirely contained by the identified section(s), theplayback tool reconstructs only the identified section(s). Or, if theview window has changed dramatically and is completely outside of theidentified section(s), the playback tool reconstructs only thelow-resolution version of the input picture.

Then, based at least in part on the reconstructed section(s) and/or thereconstructed low-resolution version of the input picture, the playbacktool creates (1580) an output picture. For example, the playback tooldetermines which portions of the output picture cannot be created usingthe reconstructed section(s) and, for any portion of the output picturethat cannot be created using the reconstructed section(s), creates thatportion of the output picture using the reconstructed low-resolutionversion of the input picture. Thus, the output picture can be createdusing only the reconstructed section(s). Or, the output picture can becreated using only the reconstructed low-resolution version of the inputpicture. Or, at least part of the output picture can be created usingthe one or more reconstructed sections, and at least part of the outputpicture can be created using the reconstructed low-resolution version ofthe input picture.

When creating the output picture, the playback tool can project thereconstructed section(s) and/or the reconstructed low-resolution versionof the input picture from an intermediate projection (e.g., sinusoidalprojection) to an output projection (e.g., screen projection). Or, whencreating the output picture, the playback tool can project thereconstructed section(s) and/or the reconstructed low-resolution versionof the input picture from an input projection (e.g., equirectangularprojection, cubemap projection, sinusoidal projection) to an outputprojection (e.g., screen projection).

The playback tool stores (1590) the output picture for output to adisplay device. The playback tool checks (1595) whether to continuedecoding and reconstruction operations and, if so, requests (1550) anddecodes (1570) encoded data for one or more sections of the next inputpicture. In this way, as part of a loop for the decoding andreconstruction pipeline, the playback tool reconstructs sectionsidentified in the view window pipeline.

The playback tool can receive one or more manifest files (e.g., from amedia server or directly from a stream configuration tool). The manifestfile(s) include information indicating, for each of the multiplebitstreams, the position of one of the multiple sections (in terms of aninput projection or spherical projection) whose content is part of thecorresponding video stream for that bitstream. For example, for eachsection, the manifest file includes phi and theta coordinates for thesection. The playback tool can use the manifest file(s) to identify(1520) the section(s) that contain at least part of the view windowand/or select (1530) the bitstream(s) for the identified sections. Theplayback tool can also use the manifest file(s) when creating (1580) theoutput picture based on the reconstructed section(s) and/orreconstructed low-resolution version of the input picture. The manifestfile(s) can also include information that indicates where thelow-resolution version of the input picture is positioned in thecomposite pictures, respectively. The manifest file(s) can be deliveredas user data of elementary bitstreams, as metadata in a container, or insome other way. Alternatively, the stream configuration tool andplayback tool(s) can operate without exchanging information in manifestfile(s), and input pictures are partitioned into sections according to astatic, pre-defined pattern.

In view of the many possible embodiments to which the principles of thedisclosed invention may be applied, it should be recognized that theillustrated embodiments are only preferred examples of the invention andshould not be taken as limiting the scope of the invention. Rather, thescope of the invention is defined by the following claims. We thereforeclaim as our invention all that comes within the scope and spirit ofthese claims.

1. A computer system comprising one or more processing units and memory,wherein the computer system implements a panoramic video streamconfiguration tool that includes: an input buffer configured to store aninput picture of panoramic video; a formatter configured to: create alow-resolution version of the input picture; split the input pictureinto multiple sections according to partition settings; create multiplecomposite pictures, each of the multiple composite pictures includingone of the multiple sections and also including the low-resolutionversion of the input picture; and add the multiple composite pictures,respectively, to corresponding video streams; one or more video encodersconfigured to encode the multiple composite pictures in thecorresponding video streams, respectively, thereby producing encodeddata for the multiple composite pictures as part of multiple bitstreamsfor the corresponding video streams, respectively; and one or moreoutput buffers configured to store the encoded data for delivery.
 2. Thecomputer system of claim 1, wherein, for each of the multiple compositepictures, the low-resolution version of the input picture is adjacentone of the multiple sections within the composite picture.
 3. Thecomputer system of claim 1, wherein, for each of the multiple compositepictures, one of the multiple sections provides a first view of a framepacking arrangement, and the low-resolution version of the input pictureprovides a second view of the frame packing arrangement.
 4. The computersystem of claim 1, wherein, for each of the multiple composite pictures,the low-resolution version of the input picture is positioned at apre-defined location relative to the one of the multiple sections in thecomposite picture.
 5. The computer system of claim 1, wherein a manifestfile includes information that indicates where the low-resolutionversion of the input picture is positioned in the multiple compositepictures, respectively.
 6. The computer system of claim 1, wherein theinput picture has a first spatial resolution, wherein the low-resolutionversion of the input picture has a second spatial resolution lower thanthe first spatial resolution, and wherein each of the multiple sectionshas a third spatial resolution lower than the first spatial resolution.7. The computer system of claim 1, wherein the input picture and thelow-resolution version of the input picture are in an input projection,and wherein the formatter is further configured to: project the inputpicture from the input projection to an intermediate projection, themultiple sections being in the intermediate projection.
 8. The computersystem of claim 7, wherein the input projection is an equirectangularprojection, and wherein the intermediate projection is a sinusoidalprojection, at least one of the multiple sections including at leastsome sample values having default values not representing content of theinput picture.
 9. The computer system of claim 1, wherein the multiplebitstreams are video elementary bitstreams, and wherein the panoramicvideo stream configuration tool further includes: a multiplexer forcombining the encoded data, for the multiple bitstreams, into a singlecontainer stream.
 10. In a computer system that implements a panoramicvideo stream configuration tool, a method comprising: receiving an inputpicture of panoramic video; creating a low-resolution version of theinput picture; splitting the input picture into multiple sectionsaccording to partition settings; creating multiple composite pictures,each of the multiple composite pictures including one of the multiplesections and also including the low-resolution version of the inputpicture; adding the multiple composite pictures, respectively, tocorresponding video streams; encoding the multiple composite pictures inthe corresponding video streams, respectively, thereby producing encodeddata for the multiple composite pictures as part of multiple bitstreamsfor the corresponding video streams, respectively; and storing theencoded data for delivery.
 11. A computer system comprising one or moreprocessing units and memory, wherein the computer system implements apanoramic video playback tool that includes: a view controllerconfigured to: determine a view window for playback of panoramic video;from among multiple sections of the panoramic video, identify one ormore sections that contain at least part of the view window; and for theone or more identified sections, select one or more bitstreams amongmultiple bitstreams for corresponding video streams; a streamingcontroller configured to request encoded data, in the one or moreselected bitstreams for the one or more identified sections,respectively, for an input picture of the panoramic video, each of theone or more identified sections being part of a composite picture thatalso includes a low-resolution version of the input picture; one or moreinput buffers configured to store the encoded data; one or more videodecoders configured to decode the encoded data to reconstruct the one ormore identified sections for the input picture and/or reconstruct thelow-resolution version of the input picture; a mapper configured to,based at least in part on the one or more reconstructed sections and/orthe reconstructed low-resolution version of the input picture, create anoutput picture; and one or more output buffers configured to store theoutput picture for output to a display device.
 12. The computer systemof claim 11, wherein the view controller is configured to, in multipleiterations, perform operations to determine the view window, identifythe one or more sections that contain at least part of the view window,and, for the one or more identified sections, select the one or morebitstreams.
 13. The computer system of claim 11, wherein the mapper isfurther configured to: determine which portions of the output picturecannot be created using the one or more reconstructed sections; and forany portion of the output picture that cannot be created using the oneor more reconstructed sections, create that portion of the outputpicture using the reconstructed low-resolution version of the inputpicture.
 14. The computer system of claim 13, wherein at least part ofthe output picture is created using the one or more reconstructedsections, and wherein at least part of the output picture is createdusing the reconstructed low-resolution version of the input picture. 15.The computer system of claim 11, wherein the low-resolution version ofthe input picture and the one of the multiple sections in the compositepicture are located at pre-defined positions within the compositepicture.
 16. The computer system of claim 11, wherein a manifest fileincludes information that indicates where the low-resolution version ofthe input picture is positioned in the composite pictures, respectively.17. The computer system of claim 11, wherein the input picture has afirst spatial resolution, wherein the low-resolution version of theinput picture has a second spatial resolution lower than the firstspatial resolution, and wherein each of the multiple sections has athird spatial resolution lower than the first spatial resolution. 18.The computer system of claim 11, wherein the mapper is furtherconfigured to: when creating the output picture, project the one or morereconstructed sections from an intermediate projection to an outputprojection.
 19. The computer system of claim 18, wherein theintermediate projection is a sinusoidal projection, and wherein theoutput projection is a screen projection.
 20. The computer system ofclaim 11, wherein the mapper is further configured to: when creating theoutput picture, project the low-resolution version of the input picturefrom an input projection to an output projection.